Methods and reagents to detect and characterize norwalk and related viruses

ABSTRACT

Double-stranded cDNA was synthesized from nucleic acid extracted from Norwalk virus purified from stool specimens of volunteers. One clone was isolated from a cDNA library constructed in a pUC-13 vector after amplification of the cDNA. The specificity of this cDNA (pUCNV-953) was shown by hybridization assays. The cDNA reacted with post (but not pre-) infection stool samples from Norwalk volunteers and with highly purified Norwalk virus, but not with other common enteric viruses such as hepatitis A virus and rotavirus. Finally, the probe detected virus in the same fractions of CsCl gradients in which viral antigen was detected using a specific Norwalk virus radioimmunoassay, and particles were detected by immune electron microscopy. Single-stranded RNA probes derived from the DNA clone after subcloning into an in vitro transcription vector were also used to show that the Norwalk virus contains a ssRNA genome of about 8 kb in size. The original clone was also used to detect additional cDNAs which represent at least 7 kb of nucleic acid of the Norwalk genome. The availability of a Norwalk-specific cDNA and the first partial genome sequence information allow rapid cloning of the entire genome and of establishment of sensitive diagnostic assays. Such assays can be based on detection of Norwalk virus nucleic acid or Norwalk viral antigen using polyclonal or monoclonal antibodies to proteins expressed from the cDNA or to synthetic peptides made based on the knowledge of the genome sequence. Assays using proteins deduced from the Norwlk virus genome and produced in expression systmes can measure antibody responses. Vaccines made by recombinant DNA technology are now feasible.

This application is a continuation of U.S. application Ser. No. 08/486,049 filed Jun. 7, 1995 issued as U.S. Pat. No. 6,572,862, which is a continuation of U.S. application Ser. No. 07/696,454 filed May 6, 1991 (now abandoned), which is a continuation in part of U.S. application Ser. No. 07/433,492 filed Nov. 8, 1989 (now abandoned), U.S. application Ser. No. 07/515,933, filed Apr. 27, 1990 (now abandoned), and U.S. application Ser. No. 07/573,509 filed Aug. 27, 1990 (now abandoned).

This invention is supported in part through grants or awards from the Food and Drug Administration and the National Institute of Health.

FIELD OF THE INVENTION

The present invention relates generally to synthesizing clones of Norwalk virus and to making probes to Norwalk and related viruses. It also relates to methods of detection and characterization of Norwalk and related viruses.

BACKGROUND OF THE INVENTION

Norwalk virus is one of the most important viral pathogens causing acute gastroenteritis, the second most common illness in the United States (Dingle et al., 1953; Kapikian and Chanock, 1985). Up to 42% of cases of viral gastroenteritis have been estimated to be caused by Norwalk or Norwalk-like viruses (Kaplan et al., 1982). Both water and foodborne transmission of Norwalk virus has been documented, and particularly large epidemic outbreaks of illness have occurred following consumption of contaminated shellfish including clams, cockles, and oysters (Murphy et al., 1979; Gunn et al., 1982; Wilson et al., 1982; Gill et al., 1983; DuPont 1986; Morse et al., 1986; Sekine et al., 1989). An increase in fish and shellfish-related food poisonings has recently been noted and attributed to increased recognition of these entities by clinicians as well as to increased consumption of seafood (Eastaugh and Shepherd, 1989). Norwalk virus was discovered in 1973. However, knowledge about the virus has remained limited because it has failed to grow in cell cultures and no suitable animal models have been found for virus cultivation. Human stool samples obtained from outbreaks and from human volunteer studies, therefore, are the only source of the virus. Still the concentration of the virus in stool is usually so low that virus detection with routine electron microscopy is not possible (Dolin et al., 1972; Kapikian et al., 1972; Thornhill et al., 1975). Current methods of Norwalk virus detection include immune electron microscopy and other immunologic methods such as radio immunoassays (RIAs) or a biotin-avidin enzyme linked immunoabsorbent assays (ELISAs) which utilize acute and convalescent phase serum from humans. To date, no hyperimmune serum from animals has been successfully prepared due either to insufficient quantities or unusual properties of the viral antigen. Preliminary biophysical characterization of virions has indicated particles contain one polypeptide (Greenberg et al., 1981), but efforts to characterize the viral genome have failed. Therefore, these viruses have remained unclassified.

CITED AND RELEVANT INFORMATION

-   1. Dingle J, Badger G, Feller A et al. 1953. A study of illness in a     group of Cleveland families: 1. Plan of study and certain general     observations. Am. J. Hyg. 58:16-30. -   2. Dolin R, Blacklow N R, DuPont H, Buscho R F, Wyatt R G, Kasel J     A, Hornick R, and Chanock R M. 1972. Biological properties of     Norwalk agent of acute infectious nonbacterial gastroenteritis.     Proc. Soc. Exp. Med. and Biol. 140:578-583. -   3. Dolin R, Blacklow N R, DuPont H, Formal S, Buscho R F, Kasel J A,     Chames R P, Hornick R, and Chanock R M. 1971. Transmission of acute     infectious nonbacterial gastroenteritis to volunteers by oral     administration of stool filtrates. J. Infect. Dis. 123:307-312. -   4. DuPont H L. 1986. Consumption of raw shellfish—is the risk now     unacceptable? New Engl. J. Med. 314:707-708. -   5. Eastaugh J, Shepherd S. 1989. Infectious and toxic syndromes from     fish and shellfish consumption. Arch. Intern. Med. 149:1735-1740. -   6. Gill O N, Cubitt W D, McSwiggan D A, Watney B M and Bartlett C     L R. 1983. Epidemic of gastroenteritis caused by oysters     contaminated with small round structured virus. Br. Med. J.     287:1532-1534. -   7. Greenberg H B, Valdesuso J R, Kalica A R, Wyatt R G, McAuliffe V     J, Kapikian A Z and Chanock R M. 1981. Proteins of Norwalk virus. J.     Virol. 37: 994-999. -   8. Gunn R A, Janowski H T, Lieb S, Prather E C, and Greenberg     H B. 1982. Norwalk virus gastroenteritis following raw oyster     consumption. Am. J. Epidemiol. 115:348-351. -   9. Jiang X, Estes M K, and Metcalf T G. 1989. In situ hybridization     for quantitative assay of infectious hepatitis A virus. J. Clin.

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-   10. Jiang X, Estes M K, and Metcalf T G. 1987. Detection of     hepatitis A virus by hybridization with single-stranded RNA probes.     Appl. Environ. Microbiol. 53:2487-2495. -   11. Jiang X, Estes M K, Metcalf T G, and Melnick J L. 1986.     Detection of hepatitis A virus in seeded estuarine samples by     hybridization with cDNA probes. Appl. Environ. Microbiol.     52:711-717. -   12. Kapikian A Z and Chanock R M. 1990. Norwalk group of viruses.     In: B N Fields (ed.) Virology, Raven Press, New York, pp. 671-693. -   13. Kapikian A Z, Wyatt R G, Dolin R. Thornhill T S, Kalica A R, and     Chanock R M. 1972. Visualization by immune electron microscopy of a     27-nm particle associated with acute infectious nonbacterial     gastroenteritis. J. Virol. 10:1075-1081. -   14. Kaplan J, Feldman R, Campbell D et al. 1982. Epidemiology of     Norwalk Gastroenteritis and the Role of Norwalk Virus in Outbreaks     of Acute Nonbacterial Gastroenteritis. Ann. Internal Med. 96(6):     756-761. -   15. Morse D L, Guzewich J J, Hanrahan J P, Stricof R, Shayegani M,     Deibel R, Grabau J C, Nowak N A, Herrmann J E, Cukor G, and Blacklow     NR. 1986. Widespread outbreaks of clam and oyster-associated     gastroenteritis: role of Norwalk virus. New Engl. J. Med.     314:678-681. -   16. Murphy A M, Grohmann G S, Christopher P J, Lopez W A, Davey G R,     and Millsom R H. 1979. An Australia-wide outbreak of gastroenteritis     from oysters caused by Norwalk virus. Med. J. Aust. 2:329-333. -   17. Sekine S, Okada S, Hayashi Y, Ando T, Terayama T, Yabuuchi K,     Miki T, and Ohashi M. 1989. Prevalence of small round structured     virus infections in acute gastroenteritis outbreaks in Tokyo.     Microbiol. Immunol. 33:207-217. -   18. Thornhill T S, Kalica A R, Wyatt R G, Kapikian A Z, and Chanock     R M. 1975. Pattern of shedding of the Norwalk particle in stools     during experimentally induced gastroenteritis in volunteers as     determined by immune electron microscopy. J. Infect. Dis. 132:28-34. -   19. Wilson R, Anderson M J, Holman R C, Gary G W, and Greenberg     H B. 1982. Waterborne gastroenteritis due to the Norwalk agent:     clinical and epidemiologic investigation. Am. J. Public Health     72:72-74. -   20. Hayashi Y, Ando T, Utagawa E, Sekine S, Okada S, Yabuuchi K,     Miki T, and Ohashi M. 1989. Western Blot (Immunoblot) Assay,     Round-Structured Virus Associated with an Acute Gastroenteritis     Outbreak in Tokyo. J. Clin. Microbiol. 27:1728-1733. -   21. U.S. Pat. No. 4,358,535, issued Nov. 9, 1982, to Fahkow S and     Moseley S L. Specific DNA Probes in Diagnostic Microbiology. -   22. U.S. Pat. No. 4,751,080, issued Jun. 14, 1988, to Wyatt R G,     Kapikian A Z, Chanock R M, Midthum K, Flores J, Hoshino Y. Vaccine     Against Rotavirus Diseases. -   23. U.S. Pat. No. 4,814,268, issued Mar. 21, 1989, to Kreider J W     and Howett M. K. Methods for Propagating Fastidious Human Viruses     and for Producing Purified Suspensions Thereof.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to characterize the Norwalk and related virus genomes by synthesizing and cloning a cDNA library.

It is an associated object of the invention to deduce amino acid sequences from the cDNA.

Another object of the invention is to develop a method of preparing polyclonal and monoclonal antibodies to the Norwalk and related viruses.

Still another object of the invention is to develop a method of making probes to detect Norwalk and related viruses.

A further object of the invention is to use the cDNA or fragments or derivatives thereof in assays to detect Norwalk and related viruses in samples suspected of containing the viruses.

A still further object of the invention is to express proteins to measure antibody responses.

A nucleotide sequence of the genome sense strand of the Norwalk virus cDNA clone according to the presently preferred embodiment of the invention intended to accomplish the foregoing objects includes the nucleotide sequence shown in Table 1. Within the nucleotide sequence are regions which encode proteins. The nucleotide sequence of the Norwalk virus genome, its fragments and derivatives are used to make diagnostic products and vaccines.

Other and still further objects, features and advantages of the present invention will be apparent from the following description of a presently preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. EM picture of Norwalk viruses after CsCl gradient purification.

FIG. 2 a. Hybridization of stool samples with ³²P-labeled plasmid DNA for screening positive Norwalk cDNA clones. Nucleic acids from paired stools [before (b) and after (a) infection with Norwalk virus] from two volunteers (1 and 2) were dotted on Zetabind filters. Replicate strips were prepared and hybridized at 50° C. and 65° C. with each test clone (pUC-27, pUC-593, pUC-13 and pUCNV-953). One clone (pUCNV-953) which reacted only with stool samples after (but not before) Norwalk infection was considered as a potential positive clone and was chosen for further characterization.

FIG. 2 b. Dot blot hybridization of clone ³²P-labeled pUCNV-953 with another 3 sets of stool samples collected at different times after infection (B=before acute phase of illness; A=acute phase of illness; P=post-acute phase of illness) of 3 volunteers. The nucleic acids were dotted directly or after treatment with RNAse or with DNAse before dotting. Double-stranded homologous cDNA (pUCNV-953) was dotted after the same treatments as the stool samples.

FIG. 3 a. Dot blot hybridization of Norwalk viruses in a CsCl gradient with ssRNA probes made from pGEMNV-953. Aliquots of 50 ul from each fraction in a CsCl gradient were dotted onto a Zetabind filter. Duplicates of filters were made and hybridized with the two ssRNA probes respectively. The two strands were subsequently called cRNA (positive hybridization with the viral nucleic acid) and vRNA (no hybridization with the viral nucleic acid, data not shown). The graph shows EM counts of Norwalk viruses from each fraction of the same CsCl gradient for the dot blot hybridization. Five squares from each grid were counted and the average of the number of viral particles per square was calculated.

FIG. 4. Hybridization of Norwalk viral RNA with ³²P-labeled clone pUCNV-953. Nucleic acids extracted from partially purified viruses were electrophoresed in a native agarose gel as described previously (Jiang et al., 1989). The gel was then dried at 80° C. for 1 h and hybridized with ³²P-labeled pUCNV-953 insert. Lane 1, 23 S and 16 S rRNA from E. coli (Miles Laboratories Inc., Naperville, Ill. 60566), lanes 2 and 4, total nucleic acids from partially purified stool samples containing Norwalk virus, and lane 3, HAV RNA.

FIG. 5. The nucleotide sequence of the genome sense strand of the first Norwalk virus cDNA clone. The deduced amino acid sequence of a long open reading frame in this cDNA is also shown.

FIG. 6. Physical map of Norwalk virus specific clones isolated from the pUC-13 library. This map assumes the Norwalk genome is 8 kb and shows only a subset (the four largest) of ^(˜)100 characterized clones. cDNAs which represent at least 7 kb of nucleic acid have been identified by hybridization with pre- and post infected stool samples, or by rescreening the library with 5′-end probes of the original (pUCNV-953) and subsequent positive clones. A poly(A) tail (^(˜)80 bases) is present at the 3′-end of clone pUCNV-4145. Clone pUCNV-1011 also hybridized specifically with post (but not pre-) infection stools from volunteers (see FIG. 7).

FIG. 7. Dot blot hybridization of stool samples with ³²P-labeled probes representing the 3′- and 5′-end of the Norwalk viral genome. Stool samples were collected from 5 human volunteers at different times (a-e) after infection with Norwalk virus. Samples in column (a) were collected in the first 24 h post-infection, before symptoms appeared. The rest of the stool samples were collected from day 2 to day 5 post-infection. Nucleic acids were extracted and duplicate dots were immobilized on a Zetabind filter. The 3′- and 5′-end probes were derived from clones pUCNV-953 and pUCNV-1011, respectively (see FIG. 6 for description of clones).

FIG. 8. Norwalk virus encodes an RNA-directed RNA polymerase sequence motif. The deduced amino acid sequence of a portion of Norwalk virus pUCNV-4095 (NV) is compared with consensus amino acid residues thought to encode putative RNA-directed RNA polymerases of hepatitis E virus (HEV), hepatitis C virus (HCV), hepatitis A virus (HAV), Japanese encephalitis virus (JE), poliovirus (polio), foot-and-mouth disease virus (FMD), encephalomyocarditis virus (EMC), Sindbis virus (SNBV), tobacco mosaic virus (TMV), alfalfa mosaic virus (AMV), brome mosaic virus (BMV), and cowpea mosaic virus (CpMV). Sequences for viruses other than NV are from FIG. 3 of Reyes et al., Science 247:1335-1339.

FIG. 9. Three sets of primers used to amplify the Norwalk virus genome.

FIG. 10. This schematic shows the organization of Norwalk genome shown in Table 1. The features shown here are based on analyses of the nucleotide sequence of the Norwalk virus genome and the deduced amino acid sequence of proteins encoded in the genome. The genome contains 7753 nucleotides including A's at the 3′-end. Translation of the sequence predicts that the genome encodes three open reading frames (shown by the open boxes). The first open reading frame is predicted to start from an initiation codon at nucleotide 146 and it extends to nucleotide 5359 (excluding the termination codon). The second open reading frame is initiated at nucleotide 5346 and it extends to nucleotide 6935, and a third open reading frame exists between nucleotides 6938 and 7724. Based on comparisons of these predicted proteins with other proteins in the protein databank, the first open reading frame is a protein that is eventually cleaved to make at least three proteins. These three proteins include a picornavirus 2C-like protein, a 3C-like protease and an RNA-dependent RNA polymerase. The second frame encodes the capsid protein.

FIG. 11. Expression of the Norwalk virus capsid protein. Baculovirus recombinants (C-6 and C-8) that contain a subgenomic piece of Norwalk virus DNA (from nucleotides 5337 to 7724) were selected and used to infect insect (Spodoptera fugiperda) cells at a multiplicity of infection of 10 PFU/cell. After 4 days of incubation at 27° C., the infected cells were harvested and the proteins were analyzed by electrophoresis on 12% polyacrylamide gels. The proteins were visualized after staining with Coomassie blue. The Norwalk-expressed protein (highlighted by the arrow) is only seen in the recombinant-infected cells, but no in wild-type baculovirus (wt) or mock-infected insect cells.

FIG. 12. The Norwalk virus expressed protein shows immunoreactivity with sera from volunteers infected with Norwalk virus. The expressed protein shown in FIG. 11 was absorbed onto the wells of a 96-well ELISA plate and its reactivity was tested with dilutions of serum samples taken from volunteers before (pre) and three weeks after (post) infection with Norwalk virus. After an incubation at 37° C. for 2 hours, a peroxidase-conjugated goat-anti-human IgG, IgM and IgA serum was added and reactivity was subsequently observed by reading the optical density at 414 nm after addition of the substrate. The data show that post-infection sera reacted strongly with the expressed antigen at serum dilutions of 1:100 and 1:1000, and some sera were still reactive at a dilution of 1:1000.

FIG. 13. Baculovirus recombinants containing the 3′-end of the Norwalk genome produce virus-like particles in insect cells. Lysates from insect cells infected with baculovirus recombinant C-8 were analyzed by electron microscopy and shown to contain numerous virus-like particles. These particles are the same size as virus particles obtained from the stools of volunteers infected with Norwalk virus. Bar=50 nm.

FIG. 14. Norwalk virus-like particles can be purified in gradients of CsCl. Supernatants of insect cells infected with the baculovirus recombinant C-8 were processed by extraction with genetron and PEG precipitation and virus eluted from these PEG pellets was centrifuged in CsCl gradient in a SW50.1 rotor for 24 hours at 4° C. The gradient was fractionated and material in each fraction was adsorbed onto two wells of an ELISA plate. Duplicate wells were then treated either with pre- or post-infection serum, peroxidase-conjugated goat anti-human serum and substrate and the reactions were monitored by reading the OD414 nm. A peak was observed in the gradient at a density of 1.31 g/cm³ and this peak was shown to contain virus-like particles by electron microscopy. This peak also contained a major protein of an approximate molecular weight of 58,500 that comigrated with the protein expressed in the insect cells from the same baculovirus recombinant.

FIG. 15. Use of the expressed virus-like particles to measure the reactivity of pre- and post-serum samples from volunteers infected with Norwalk virus shows that most volunteers have an immune response. Volunteer 6 who did not show an immune response also did not become ill after being administered virus.

DETAILED DESCRIPTION OF THE INVENTION

It is readily apparent to one skilled in the art that various substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

The term “fragment” as used herein is defined as a fragment of a genome or a subgenomic clone that is required to be expressed to produce a peptide fragment which might be able to induce a polyclonal or monoclonal antibody. It is possible a peptide of only 5 amino acids could be immunogenic but usually peptides of 15 amino acids or longer are required. This depends on the properties of the peptide and it cannot be predicted in advance.

The term “derivative” as used herein is defined as larger pieces of DNA or an additional cDNA which represents the Norwalk genome and which is detected by direct or sequential use of the original cDNA and any deduced amino acid sequences thereof. Clone pUCNV-1011, therefore, is a derivative, although it does not overlap or share sequences with the original clone. Also included within the definition of derivative are RNA counterparts of DNA fragments and DNA or cDNA fragments in which one or more bases have been substituted or to which labels and end structures have been added without affecting the reading or expression of the DNA or cDNA.

Production of Norwalk Virus for Molecular Cloning

Norwalk virus was produced by administration of safety tested Norwalk virus (8FIIa) to adult volunteers. The virus inoculum used in the volunteer study, was kindly supplied by Dr. Albert Kapikian (Laboratory of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md.). This virus originated from an outbreak of acute gastroenteritis in Norwalk, Ohio (Dolin et al., 1971). Two ml of a 1 to 100 dilution of 8FIIa in TBS was administered orally to each individual with 80 ml of milli-Q water (Millipore, Bedford, Mass. 01730). Sodium bicarbonate solution was taken by each person 2 minutes before and 5 minutes after virus administration. The volunteer studies were approved by the Institutional Review Board for Human Research at Baylor College of Medicine, at the Methodist Hospital and at the General Clinical Research Center. The virus was administered to the volunteers in the General Clinical Research Center where the volunteers were hospitalized and under extensive medical care for 4 days. All stools were collected and kept at −70° C. for later use.

Purification of Norwalk Viruses from Stool Samples

A 10% solution of stool samples in TBS was clarified by low speed centrifugation at 3000 rpm for 15 min. The resultant supernate was then extracted two to three times with genetron in the presence of 0.5% Zwittergent 3-14 detergent (Calbiochem Corp., La Jolla, Calif.). Viruses in the aqueous phase were concentrated by pelleting at 36,000 rpm for 90 minutes through a 40% sucrose cushion in a 50.2 Ti rotor (Beckman Instruments, Inc., Palo Alto, Calif. 94304). The pellets were suspended in TBS and mixed with CsCl solution (refractive index 1.368) and centrifuged at about 35,000 rpm for about 24 h in a SW50.1 rotor (Beckman). The CsCl gradient was fractionated by bottom puncture and each fraction was monitored for virus by EM examination. The peak fractions containing Norwalk virus were pooled and CsCl in the samples was diluted with TBS and removed by pelleting the viruses at about 35,000 rpm for 1 h. The purified virus was stored at about −70° C.

Extraction of Nucleic Acids from Purified Virus

One method of extraction involved treating purified Norwalk virus from CsCl gradients with proteinase K (400 ug/ml) in proteinase K buffer (0.1 M Tris-Cl pH 7.5, 12.5 mM EDTA, 0.15 M NaCl, 1% w/v SDS) at about 37° C. for about 30 min. The samples were then extracted once with phenol-chloroform and once with chloroform. Nucleic acids in the aqueous phase were concentrated by precipitation with 2.5 volumes of ethanol in the presence of 0.2 M NaOAc followed by pelleting for 15 min in a microcentrifuge.

cDNA Synthesis and Cloning of Amplified of cDNA

One method of synthesis and cloning included denaturing nucleic acids extracted from the purified Norwalk viruses with 10 mM CH₃HgOH. Then cDNA was synthesized using the cDNA synthesis kit with the supplied random hexanucleotide primer (Amersham, Arlington Heights, Ill. 60005). After the second strand synthesis, the reaction mixture was extracted once with phenol-chloroform and once with chloroform followed by ethanol precipitation. Amplification of DNA was performed using the random prime kit for DNA labeling (Promega Corp., Madison, Wis. 53711-5305). Eight cycles of denaturation (100° C. for 2 min), reannealing (2 min cooling to room temperature) and elongation (room temperature for 30 min) were performed after addition of Klenow fragment (Promega Corp.). A DNA library was constructed in pUC-13 with blunt-end ligation into the Sma I site.

Screening of the Library for Positive Clones

As one method of screening, white colonies from transformed DH5 alpha bacterial cells (BRL) were picked and both a master plate and minipreps of plasmid DNA were prepared for each clone. Clones containing inserts were identified after electrophoresis of the plasmid DNA in an agarose gel. The insert DNA in the agarose gel was cut out and labeled with ³²P using random primers and Klenow DNA polymerase such as in the prime-a-gene® labeling system (Promega Corp.). Other isotopic or biochemical labels, such as enzymes, and fluorescent, chemiluminescent or bioluminescent substrates can also be used. Nucleic acids extracted from paired stool samples (before and after Norwalk infection) from two volunteers (543 and 544) were dotted onto Zetabind filters (AFM, Cuno, Meriden, Conn.). Replicate filter strips were prepared and hybridized with each labeled plasmid probe individually at 65° C. without formamide. Potential positive clones were judged by their different reactions with the pre- and post-infection stools. Clones which reacted with post (but not pre-) infection stools of volunteers were considered positive and these clones on the master plates were characterized further. Once one Norwalk clone was identified, it was used to rescreen the cDNA library to identify additional overlapping clones. Rescreening the cDNA library with these additional clones can ultimately identify clones representing the entire Norwalk virus genome.

The following examples are offered by way of illustration and are not intended to limit the invention in any manner.

EXAMPLE 1 Electron Micrograph Confirmation

To permit better diagnosis and molecular characterization of Norwalk virus, a cDNA library was derived from nucleic acid extracted from virions purified from stool samples. Norwalk virus was purified with methods used previously for hepatitis A and rotaviruses from stool samples with some modifications (Jiang et al., 1986). Basically stool samples obtained from volunteers administered Norwalk virus were treated with Genetron to remove lipid and water insoluble materials. Virus in the aqueous phase was then pelleted through a 40% sucrose cushion. The resultant pellets were resuspended, sonicated and loaded in a CsCl gradient for isopycnic centrifugation. FIG. 1 shows an electron micrograph of purified Norwalk viruses after CsCl gradient centrifugation. Approximately 10⁹ physical particles were obtained from 500 grams of stools when the first cDNA library was made.

EXAMPLE 2 Initial cDNA Synthesis, Cloning and Screening

A cDNA library was generated from nucleic acids extracted from these purified viruses by proteinase K treatment of the samples followed by phenol-chloroform extraction and ethanol precipitation (Jiang et al., 1986; 1987). Because the nature of the viral genome was unknown, the extracted nucleic acids were denatured with methylmercuric hydroxide before cDNA synthesis. Random primed cDNA was synthesized with the Gubler-Hoffman method (cDNA synthesis system plus, Amersham) and a small amount of cDNA was obtained. Direct cloning of this small amount of cDNA was unsuccessful. Therefore, a step of amplification of the DNA was performed by synthesizing more copies of the DNA with random primers and the Klenow fragment of DNA polymerase before cloning. The procedure involved cycles of denaturation, addition of random primers and the Klenow fragment of DNA polymerase, reannealing and elongation. With this procedure, a linear incorporation of labeled nucleotides into product was observed as the number of cycles of synthesis was increased. The numbers of cycles performed were limited (<10) to avoid the synthesis of an excess of smaller fragments. In the case of Norwalk cDNA, 8 cycles of amplification were performed and approximately 2.5 ug of DNA were obtained, which was at least a 100-fold amplification of the starting template cDNA. This amplified cDNA was cloned into pUC-13 by blunt-end ligation and a positive clone (pUCNV-953) was isolated.

To obtain the positive Norwalk virus clone, minipreparations of the plasmid DNAs containing potential inserts were screened by agarose gel electrophoresis. Inserts of the larger clones in the gel were cut out and probes were made with the DNA in the gel using the prime-a-gene® labeling system (Promega Corp.). These probes were hybridized individually with paired stool samples (before and after Norwalk infection) from two volunteers (FIG. 2 a). One clone (pUCNV-953) reacted with post- but not pre-infection stool samples from both volunteers.

EXAMPLE 3 Confirmation of Viral Origin of the Clone pUCNV-953

To further confirm the viral origin of the clone pUCNV-953, 6 more paired stool samples were tested and the same results were obtained. FIG. 2 b shows a dot blot hybridization of the clone with stool samples collected at different times post-infection of the disease. Strong signals were observed only with stools from acute phase, but not before and after the illness. This result was consistent with previous RIA assays for viral antigen detection using convalescent sera from volunteers with Norwalk diarrhea and immune electron microscopy (IEM) studies of the samples for viral particle examination. This result also agrees with the patterns of virus shedding in stool in the course of the disease (Thornhill et al., 1975). When the clone was hybridized with fractions of a CsCl gradient from the Norwalk virus purification scheme, a correlation between hybridization and EM viral particle counts was observed (FIG. 3). The peaks of the hybridization signals and viral particle counts both were at fractions with a density of 1.38 g/cm³, which agrees with previous reports of the biophysical properties of Norwalk virus. Finally, the clone was tested by hybridization with highly purified Norwalk virus electrophoresed on an agarose gel. A single hybridization band was observed with Norwalk virus but not with HAV (FIG. 4) and rotavirus (not shown). Sequence analysis of the pUCNV-953 cDNA showed this clone is 511 bp (FIG. 5). This partial genomic cDNA encodes a potential open reading frame for which the amino acid sequence has been deduced (FIG. 5). No significant nucleotide or deduced amino acid sequence homology was found by comparison with other sequences in the Gen Bank (Molecular Biology Information Resource, Eugene Software, Baylor College of Medicine).

EXAMPLE 4 Use of Norwalk Virus cDNA to Characterize the Viral Genome

The pUCNV-953 cDNA was subcloned into the transcription vector pGEM-3Zf(+) and grown. ssRNA probes were then generated by in vitro transcription using SP6 and T7 polymerases (Promega). When two opposite sense ssRNA probes were hybridized with the viral nucleic acid separately, only one strand reacted with the virus, indicating the viral genome is single-stranded. As shown in FIG. 2 b, the hybridization signals were removed by treatment of the viral nucleic acid with RNAse (but not with DNAse) before loading them onto the filters, indicating the virus genome contains ssRNA. A long open reading frame was found in one of the two strands of the inserted DNA by the computer analysis of the sequences of pUCNV-953. The ssRNA probe with the same sequence as this coding strand does not react with the viral nucleic acid, but the complementary ssRNA probe does react in the hybridization tests. Therefore, Norwalk virus contains a positive sense single-stranded RNA genome. The size of the genome of Norwalk virus was estimated to be about 8 kb based on comparisons of the migration rate of the purified viral RNA in agarose gels with molecular weight markers. This size is slightly bigger than that of the picornaviruses [HAV and poliovirus; (FIG. 4)].

The pUCNV-953 cDNA was used to rescreen a second cDNA library made as follows. A clone of the Norwalk or related virus was synthesized by isolating nucleic acid from purified Norwalk virus; cDNA was synthesized using reverse transcriptase and random primers; a second strand of DNA was synthesized from the cDNA; and at least one copy of DNA was inserted into a plasmid or a cloning and expression vector; and screening the library with the original puCNV-953 cDNA identified clones containing fragments of (or the complete) Norwalk or related genome. Alternatively at least one copy of DNA was inserted in a cloning and expression vector, such as lambda ZAPII® (Stratigene Inc.), and the cDNA library was screened to identify recombinant phage containing fragments of or the complete Norwalk or related genome. Additional cDNAs were made and found with this method. Use of these additional cDNAs to rescreen the library resulted in detection of new clones (FIG. 6). Use of the original pUCNV-953 and one additional non-overlapping cDNA (pUCNV-1011) as probes confirmed they detected virus (FIG. 7). Other overlapping cDNA (pUCNV-4145) and non-overlapping cDNA (pUCNV-4095) are useful probes to detect the Norwalk and related viruses.

Thus, the cDNA, or fragments or derivatives thereof, can be used in assays to detect the genome of Norwalk and other related viruses. The detection assays include labeled cDNA or ssRNA probes for direct detection of the Norwalk virus genome and measurement of the amount of probe binding. Alternatively, small oligonucleotide probes (10 nucleotides or greater) and polymerase chain reaction amplification are used to detect the Norwalk and related virus genomes. Expression of the open reading frame in the cDNA is used to make hyperimmune or monoclonal antibodies for use in diagnostic products and vaccines.

Using the above methodology, the nucleotide sequence in Table 1 was identified. Within that nucleotide sequence, the encoding regions for several proteins have been identified. In that sequence, the first protein is encoded by nucleotides 146 through 5339 and the amino acid sequence is shown in Table 2. This first protein is eventually cleaved to make at least three proteins including a picornavirus 2c-like protein, a 3C-like protease and an RNA-dependent RNA polymerase. The fact that this portion of the genome contains an RNA polymerase is verified by comparisons with RNA polymerase in other positive sense RNA viruses (FIG. 8).

Also in the sequence in Table 1, two other protein encoding regions were found. They are encoded by nucleotides 5346 through 6935 and nucleotides 6938 through 7724. The amino acid sequences for these two proteins are shown in Tables 3 and 4, respectively.

EXAMPLE 5 Diagnostic Assays Based on Detection of the Sequences of the Norwalk Virus Genome

Hybridization assays are the assays of choice to detect Norwalk virus because small amounts of virus are present in clinical or contaminated water and food specimens. Previously, the possibility to detect Norwalk and related nucleic acids was not possible because the genome of Norwalk virus was not known and no sequence information was available. Probes made from the Norwalk virus cDNA or primers made from the Norwalk virus genome sequence allow methods to amplify the genome for diagnostic products to be established. Probes to identify Norwalk virus alone and to identify other viruses in the Norwalk group enable development of either specific assays for Norwalk or general assays to detect sequences common to many or all of these agents.

In the past, one major difficulty encountered in RT-PCR detection of viral RNA in stool samples was that uncharacterized factor(s) are present in stools which inhibit the enzymatic activity of both reverse transcriptase and Taq polymerase (Wilde et al., J Clin Microbiol 28:1300-1307, 1990). These factor(s) were difficult to remove by routine methods of nucleic acid extraction. Techniques were developed using cetyltrimethylammonium bromide (CTAB) and oligo d(T) cellulose to specifically separate viral RNA from the inhibitory factor(s). These techniques were based on the unique properties of CTAB which selectively precipitates nucleic acid while leaving acid insoluble polysaccharide in the supernatant. The resulting nucleic acid was further purified by adsorption onto and elution from oligo d(T) cellulose. This step removes unrelated nucleic acids that lack a poly(A) tail. With this technique, Norwalk virus was detected easily by PCR in very small amounts (400 ul of a 10% suspension) of stool sample. For example, one skilled in the art will recognize that it is now possible to clone the genome of RNA viruses present in low concentrations in small amounts of stool after RT-PCR and a step of amplification of the viral RNA by RT-PCR using random primers. In some cases, RT-PCR active nucleic acids are extracted with CTAB and without oligo d(T) cellulose. In addition, now that the inhibitor(s) can be removed from stool, it will also be possible to detect and clone nucleic acids of other viruses (DNA viruses, non-poly(A) tailed RNA viruses) present in stool.

The CTAB and oligo d(T) cellulose technique of extraction followed by detection of viral RNA with RT-PCR was used on stool samples and could be used on water and food samples. Stool sample was suspended in distilled water (about 10% wt/vol) and extracted once with genetron. Viruses in the supernatant were precipitated with polyethylene glycol at a final concentration of about 8%. The viral pellets were treated with proteinase K (About 400 ug/ml) in the presence of SDS at about 37° C. for about 30 min. followed by one extraction with phenol chloroform and one with chloroform. A solution of about 5% CTAB and about 0.4M NaCl was added at a ratio of sample:CTAB=about 5:2. After incubation at about room temperature for about 15 min and at about 45° C. for about 5 min, the nucleic acids (including the viral RNA) were collected by centrifugation in a microcentrifuge for about 30 min. The resultant pellets were suspended in about 1M NaCl and extracted twice with chloroform. The viral RNA in the aqueous phase was used directly in RT-PCR reactions or further purified by adsorption/elution on oligo d(T) cellulose.

A batch method of adsorption/elution on oligo d(T) cellulose was used to purify poly(A) tailed RNA. In this procedure, nucleic acids partially purified as described above or RNA extracted directly with phenol chloroform (without CTAB treatment) were mixed with oligo d(T) cellulose (about 2-4 mg/sample) in a binding buffer (about 0.5M NaCl and 10 mM Tris, pH 7.5). The mixture was incubated at about 4° C. for about 1 hr with gentle shaking and then centrifuged for about 2 min in a microcentrifuge. The oligo d(T) cellulose pellet was washed 3-4 times with binding buffer and then the poly(A) tailed RNA was eluted with 1×TE buffer (about 1 mM Tris, 1 mM EDTA, pH 7.5). The supernate was collected following centrifugation to remove the oligo d(T) cellulose and the viral RNA in the supernate was precipitated with ethanol. The RNA obtained at this stage was basically inhibitor-free and able to be used in RT-PCR.

In preliminary experiments, Norwalk virus RNA was detected in less than 0.05 g of stool samples using the CTAB technique. A trace inhibitor activity was observed with RNA extracted with either CTAB or oligo d(T) alone, but this was easily removed by dilution (1:2) of the extracted nucleic acid before RT-PCR. Combination of the CTAB and oligo d(T) techniques resulted in obtaining high quality, inhibitor free RNA which could be used directly for RT-PCR detection and for cloning of the viral genome. With development of this method to clone from small amounts of stool, one skilled in the art will know that we will now be able to obtain cDNAs for the remainder of the genome including those representing the 5′-end of the genome.

For detection with PCR, primers based on the above nucleotide sequence of the genome were made by chemical methods. These primers include: Primer 1: CACGCGGAGGCTCTCAAT located at nucleotides 7448 to 7465; Primer 4: GGTGGCGAAGCGGCCCTC located at nucleotides 7010 to 7027; Primer 8: TCAGCAGTTATAGATATG located at nucleotides 1409 to 1426; Primer 9: ATGCTATATACATAGGTC located at nucleotides 612 to 629; Primer 16: CAACAGGTACTACGTGAC located at nucleotides 4010 to 4027; and Primer 17: TGTGGCCCAAGATTTGCT located at nucleotides 4654 to 4671. These primers have been shown to be useful to detect virus using reverse transcription and polymerase chain reaction methods (RT-PCR). FIG. 9 shows data using these primers. In primer sets 1 and 4, 8 and 9, and 16 and 17, the reverse compliments for the sequences given above for primers 1, 8, and 17 were used.

EXAMPLE 6 Preparation of Polyclonal Antibodies and Monoclonal Antibodies to Norwalk Virus Proteins

Protein(s) encoded in the cDNA fragments or derivatives thereof, is produced in a prokaryotic or eukaryotic expression system and used to immunize animals to produce polyclonal antibodies for diagnostic assays. Prokaryotic hosts may include Gram negative as well as Gram positive bacteria, such as E. coli, S. tymphimurium, Serratia marcescens, and Bacillus subtilis. Eukaryotic hosts may include yeast, insect or mammalian cells. Immunized animals may include mammals such as guinea pigs, mice, rabbits, cows, goats or horses or other non-mammalian or non-murine species such as chickens. Repeated immunization of these animals with the expressed protein mixed with an adjuvant such as Freund adjuvant to enhance stimulation of an immune response produces antibodies to the protein.

Alternatively, synthetic peptides of greater than 15 amino acids made to match the amino acid sequence deduced from the partial cDNA sequence (or from other sequences determined by sequencing additional cDNAs detected with the original or other clones) are linked to a carrier protein such as bovine serum albumin or lysozyme or cross-linked with treatment with gluteraldehyde and used to immunize animals to produce polyclonal antibodies for diagnostic tests.

The serum of animals immunized with either the expressed protein or with synthetic peptides are tested by immunologic assays such as immune electron microscopy, Western blots (immunoblots) and blocking ELISAs to demonstrate that antibodies to Norwalk and related viruses have been made. Reactivities with the expressed protein or synthetic peptides show specificity of the polyclonal sera. Reactivities with other viruses in the Norwalk group (Snow Mountain Agent, Hawaii Agent, Taunton Agent, etc.) indicate production of a reagent which recognizes cross-reacting epitopes.

Balb\c mice injected with the immunogens as described above and shown to have produced polyclonal antibodies are boosted with immunogen and then sacrificed. Their spleens are removed for fusion of splenocytes with myeloma cells to produce hybridomas. Hybridomas resulting from this fusion are screened for their reactivity with the expressed protein, the peptide and virus particles to select cells producing monoclonal antibodies to Norwalk virus. Screening of such hybridomas with Norwalk-related viruses permits identification of hybridomas secreting monoclonal antibodies to these viruses as well.

The novel features characteristic of this invention are set forth in the appended claims. The present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as others inherent therein. While presently preferred embodiments of the invention have been described for the purpose of disclosure, numerous changes in the details of synthesis and use described herein will be apparent to those skilled in the art. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative means of synthesis and use and equivalents falling within the spirit and scope of the invention.

Development of Diagnostic Assays

Analysis of the deduced amino acid sequence of the Norwalk virus genome has shown that the Norwalk virus has the genetic organization shown in FIG. 10. Expression of regions of this genome in cell-free translation systems and in the baculovirus expression system have shown that the 5′-end of the genome encodes nonstructural proteins and the 3′-end of the genome encodes at least one structural protein. Based on this information, one can express the complete genome or subgenomic regions of the genome to produce diagnostic assays to detect viral antigens or immune responses to specific regions of the genome. This information can be used to detect the Norwalk virus, antigens or immune responses to Norwalk virus. This information also can be used to detect other similar currently uncharacterized viruses that cause gastroenteritis or possibly other diseases. Some of these viruses will be in the Caliciviridae or in the picornavirus superfamily. All of these viruses will have matching or similar genomic regions in their DNA sequences. Examples of the diagnostic assays are shown in the specific examples and figures below.

EXAMPLE 7 Development of Diagnostic Assays to Detect Nucleic Acids of Norwalk Virus or Similar Viruses by Detection of Specific Regions of the Viral Genomes Based on an Understanding of the Norwalk Genome

The genetic organization of the Norwalk virus genome allows the prediction of specific regions of the gene sequence as regions where oligonucleotide primers or probes can be developed to detect Norwalk virus sequences and common sequences of other related or similar viruses. Some of these common genome sequences will be found in viruses in the Caliciviridae or in the picornavirus superfamily. The detection can be done by standard PCR, hybridization or other gene amplification methods.

EXAMPLE 8 Development of Diagnostic Assay Using Expressed Norwalk Virus Proteins to Detect Immune Response to Norwalk Virus

Protein(s) encoded in the Norwalk virus genome or fragments or derivatives thereof is produced in a prokaryotic or eukaryotic expression system and used as antigens in diagnostic assays to detect immune responses following virus infections. Prokaryotic hosts may include Gram negative as well as Gram positive bacteria, such as Escherichia coli, Salmonella tymphimurium, Serratia marcescens, Bacillus subtilis, Staphylococcus aureus and Streptococcus sanguinis. Eukaryotic hosts may include yeast, insect or mammalian cells. Diagnostic assays may include many format such as enzyme-linked immunosorbent assays, radioimmunoassays, immunoblots or other assays. FIG. 11 shows data for a capsid protein encoded from the 3′-end of the Norwalk virus genome. It is expressed by nucleotides 5337 through 7753 of the DNA sequence shown in Table 1 and FIG. 10. This protein has an approximate molecular weight of 58,500 and is hereinafter referred to as the 58,500 mwt protein. It was produced in insect cells infected with baculovirus recombinants (C-6 and C-8). A band (see arrow in FIG. 11) representing the 58,500 mwt protein in C-6 and C-8 infected cells is not seen in insect cells infected with wild-type (WT) baculovirus or in mock infected cells. Other proteins encoded by Norwalk virus cDNA or fragments or derivatives are similarly expressed using baculovirus recombinants and other expression systems.

FIG. 12 shows data using the 58,500 mwt protein produced using the baculovirus expression system to detect immune responses before and after infection of volunteers with Norwalk virus inoculum. Antigen was put on ELISA plates and pre- and post-infection human serum was added. The data show that when an individual has had the infection, the post-serum reacts strongly to the antigen. Other proteins encoded in the Norwalk virus cDNA or fragments or derivatives thereof are similarly used to detect immune responses following Norwalk virus infection.

Some proteins have the intrinsic property of being able to form particles. The 58,500 mwt protein discussed above has that property. Particles formed from proteins are expressed in any expression system and used to produce diagnostic assays based on detection of antibody responses or immune responses. FIG. 13 shows an electron micrograph of particles produced using the baculovirus expression system from recombinants containing the 3′-end of the Norwalk genome. These particles are similar in size to the native virus particles. They are antigenic, immunoreactive and immunogenic. They differ from most of the virus particles resulting from natural infection in that many of the expressed particles lack nucleic acids.

FIG. 14 shows data on the properties of such particles following centrifugation in gradients of CsCl. The density of the particles (symbolized by closed boxes) is 1.31 g/cc which is distinct from the 1.39 g/cc density of particles purified from the original infectious Norwalk inoculum given to volunteers. The gradients were fractionated. Each fraction was put on an ELISA plate and human serum was then introduced. The open boxes show that there was no ELISA activity with the pre-infection serum. The closed diamonds show there was reactivity with the post-infection serum. Other particles made from other proteins encoded in the Norwalk virus cDNA or fragments or derivatives thereof are similarly used to detect immune responses following Norwalk virus infection.

FIG. 15 shows data using purified particles formed by the 58,500 mwt protein to detect immune responses in post-inoculation (but not pre-inoculation) serum samples of 9 volunteers infected with Norwalk virus. One of the volunteers, number 6, exhibited no symptoms of Norwalk virus infection based on monitoring clinical symptoms or measuring an immune response. Purified, expressed particles were put on ELISA plates and one pre- and one post-infection serum samples from each volunteer was added to the particles. The amount of antibody binding to the particles in each pre- and post-infection sample was measured. The data in FIG. 15 show that the expressed proteins form particles that are immunoreactive and antigenic. Other proteins encoded in the Norwalk virus cDNA or fragments or derivatives thereof are similarly used to detect immunoreactive and antigenic activity.

EXAMPLE 9 Development of Diagnostic Assays Using Expressed Norwalk Virus Expressed Antigens

Individual proteins, particles or protein aggregates formed from expression of one or more Norwalk virus genes in any prokaryotic or eukaryotic expression system are used as an immunogen or inoculate animals to produce polyclonal and monoclonal antibodies for diagnostic assays as previously described above in example 6.

Development of a Vaccine Using Norwalk Virus Expressed Antigens EXAMPLE 10

Vaccines for Norwalk virus, the Norwalk group of viruses or other small round viruses are made from an expressed Norwalk virus protein. That expressed protein could be a Norwalk virus capsid protein expressed alone or in combination with one or more other Norwalk virus proteins or self-forming particles. For example, the particles shown in FIG. 12 were produced using the baculovirus expression system. They are used as a vaccine when expressed alone or in combination with one or more other Norwalk virus proteins. Similarly, the other proteins encoded in the Norwalk virus cDNA or fragments or derivatives thereof are used as a vaccine when expressed alone or in combination with one or more Norwalk virus proteins.

Individuals are vaccinated orally, parenterally or by a combination of both methods. For parenteral vaccination, the expressed protein is mixed with an adjuvant and administered in one or more doses in amounts and at intervals that give maximum immune response and protective immunity. Oral vaccination parallels natural infection by Norwalk virus inoculum, i.e. the individual ingests the vaccine with dechlorinated water or buffer. Oral vaccination may follow sodium bicarbonate treatment to neutralize stomach activity. For example, sodium bicarbonate solution is taken by each person 2 minutes before and 5 minutes after vaccine administration.

EXAMPLE 11 Production of a Vaccine for other Agents by Using Expressed Norwalk Virus Capsids as a Carrier or Vehicle for the Expression of other Antigens or Parts of other Antigens

Identification of the region of the genome that encodes the Norwalk virus capsid protein and that forms particles following expression (i.e., regions 5346 through 6935 and 5337 through 7724) allows genetic engineering of the cDNA that encodes the capsid protein to incorporate one or more heterologous pieces of cDNA that encode antigenic epitopes. Expression of such recombinant genes produces a recombinant capsid that is antigenic, induces antibodies, and protects against Norwalk virus and its antigens, and against the heterologous epitopes or antigens.

Alternatively, the Norwalk virus capsid protein carrier is mixed with or covalently linked to one or more heterologous protein antigens or synthetic peptides containing heterologous epitopes. This mixture and covalent linkage are antigenic, induce antibodies, and protect against Norwalk virus and its antigens, and against the heterologous epitopes or antigens.

Individuals are vaccinated using the oral and parenteral methods described above in example 10.

EXAMPLE 12 Kit

Kits for detecting immune responses to Norwalk virus are prepared by supplying in a container a protein deduced from the Norwalk virus genome shown in Table 1 or fragments or derivatives thereof and produced in an expression system. For example, the protein deduced from nucleotides 1 through 7724 the protein deduced from nucleotides 146 through 5359, the protein deduced from nucleotides 5337 through 7524, the protein deduced from nucleotides 5346 through 6935, the protein deduced from nucleotides 6938 through 7724 and any combinations thereof may be used in such kits. The kit can also include controls for false positive and false negatives, reagents and sample collection devices. The kit can be equipped to detect one sample or multiple samples.

TABLE 1 The nucleotide sequence of Norwalk virus genome. GGCGTCAAAA GACGTCGTTC CTACTGCTGC TAGCAGTGAA AATGCTAACA ACAATAGTAG 60 TATTAAGTCT CGTCTATTGG CGAGACTCAA GGGTTCAGGT GGGGCTACGT CCCCACCCAA 120 CTCGATAAAG ATAACCAACC AAGATATGGC TCTGGGGCTG ATTGGACAGG TCCCAGCGCC 180 AAAGGCCACA TCCGTCGATG TCCCTAAACA ACAGAGGGAT AGACCACCAC GGACTGTTGC 240 CGAAGTTCAA CAAAATTTGC GTTGCACTGA GAGACCACAA GACCAGAATG TTAAGACGTG 300 GGATGAGCTT GACCACACAA CAAAACAACA GATACTTGAT GAACACGCTG AGTGGTTTGA 360 TGCCGGTGGC TTAGGTCCAA GTACACTACC CACTAGTCAT GAACGGTACA CACATGAGAA 420 TGATGAAGGC CACCAGGTAA AGTGGTCGGC TAGGGAAGGT GTAGACCTTG GCATATCCGG 480 GCTCACGACG GTGTCTGGGC CTGAGTGGAA TATGTGCCCG CTACCACCAG TTGACCAAAG 540 GAGCACGACA CCTGCAACTG AGCCCACAAT TGGTGACATG ATCGAATTCT ATGAAGGGCA 600 CATCTATCAT TATGCTATAT ACATAGGTCA AGGCAAGACG GTGGGTGTAC ACTCCCCTCA 660 AGCAGCCTTC TCAATAACGA GGATCACCAT ACAGCCCATA TCAGCTTGGT GGCGAGTCTG 720 TTATGTCCCA CAACCAAAAC AGAGGCTCAC ATACGACCAA CTCAAAGAAT TAGAAAATGA 780 ACCATGGCCG TATGCCGCAG TCACGAACAA CTGCTTCGAA TTTTGTTGCC AGGTCATGTG 840 CTTGGAAGAT ACTTGGTTGC AAAGGAAGCT CATCTCCTCT GGCCGGTTTT ACCACCCGAC 900 CCAAGATTGG TCCCGAGACA CTCCAGAATT CCAACAAGAC AGCAAGTTAG AGATGGTTAG 960 GGATGCAGTG CTAGCCGCTA TAAATGGGTT GGTGTCGCGG CCATTTAAAG ATCTTCTGGG 1020 TAAGCTCAAA CCCTTGAACG TGCTTAACTT ACTTTCAAAC TGTGATTGGA CGTTCATGGG 1080 GGTCGTGGAG ATGGTGGTCC TCCTTTTAGA ACTCTTTGGA ATCTTTTGGA ACCCACCTGA 1140 TGTTTCCAAC TTTATAGCTT CACTCCTGCC AGATTTCCAT CTACAGGGCC CCGAGGACCT 1200 TGCCAGGGAT CTCGTGCCAA TAGTATTGGG GGGGATCGGC TTAGCCATAG GATTCACCAG 1260 AGACAAGGTA AGTAAGATGA TGAAGAATGC TGTTGATGGA CTTCGTGCGG CAACCCAGCT 1320 CGGTCAATAT GGCCTAGAAA TATTCTCATT ACTAAAGAAG TACTTCTTCG GTGGTGATCA 1380 AACAGAGAAA ACCCTAAAAG ATATTGAGTC AGCAGTTATA GATATGGAAG TACTATCATC 1440 TACATCAGTG ACTCAGCTGG TGAGGGACAA ACAGTCTGCA GGGGCTTATA TGGCCATCTT 1500 AGATAATGAA GAAGAAAAGG CAAGGAAATT ATCTGTCAGG AATGCCGACC CACACGTAGT 1560 ATCCTCTACC AATGCTCTCA TATCCCGGAT CTCAATGGCT AGGGCTGCAT TGGCCAAGGC 1620 TCAAGCTGAA ATGACCAGCA GGATGGGTCC TGTGGTCATT ATGATGTGTG GGCCCCCTGG 1680 TATAGGTAAA ACCAAGGCAG CAGAACATCT GGCTAAAGGC CTAGCCAATG AGATACGGCC 1740 TGGTGGTAAG GTTGGGCTGG TCCCACGGGA GGCAGTGGAT CATTGGGATG GATATCACGG 1800 AGAGGAAGTG ATGCTGTGGG ACGACTATGG AATGACAAAG ATACAGGAAG ACTGTAATAA 1860 ACTGCAAGCC ATAGCCGACT CAGCCCCCCT AACAGTCAAT TGTGACCGAA TAGAAAACAA 1920 GGGAATGCAA TTTGTGTCTG ATGCTATAGT CATCACCACC AATGCTCCTG GCCCAGCCCC 1980 AGTGGACTTT GTCAACCTGG GGCCTGTTTG CCGAAGGGTG GACTTGCTTG TGTATTGCAC 2040 GGCACCTGAA GTTGAACACA CGAGGAAAGT CAGTCCTGGG GACACAACTG CACTGAAAGA 2100 CTGCTTCAAG CCCGATTTCT CACATCTAAA AATGGAGTTG GCTCCCCAAG GGGGCTTTGA 2160 TAACCAAGGG AATACCCGGT TTGGTAAGGG TGTGATGAAG CCCACCACCA TAAACAGGCT 2220 GTTAATCCAG GCTGTAGCCT TGACGATGGA GAGACAGGAT GAGTTCCAAC TCCAGGGGCC 2280 TACGTATGAC TTTGATACTG ACAGAGTAGC TGCGTTCACG AGGATGCCCC GAGCCAACGG 2340 GTTGGGTCTC ATATCCATGG CCTCCCTAGG CAAAAAGCTA CGCAGTGTCA CCACTATTGA 2400 AGGATTAAAG AATGCTCTAT CAGGCTATAA AATATCAAAA TGCAGTATAC AATGGCAGTC 2460 AAGGGTGTAC ATTATAGAAT CAGATGGTGC CAGTGTACAA ATCAAAGAAG ACAAGCAAGC 2520 TTTGACCCCT CTGCAGCAGA CAATTAACAC GGCCTCACTT GCCATCACTC GACTCAAAGC 2580 AGCTAGGGCT GTGGCATACG CTTCATGTTT CCAGTCCGCC ATAACTACCA TACTACAAAT 2640 GGCGGGATCT GCGCTCGTTA TTAATCGAGC GGTCAAGCGT ATGTTTGGTA CCCGTACAGC 2700 AGCCATGGCA TTAGAAGGAC CTGGGAAAGA ACATAATTGC AGGGTCCATA AGGCTAAGGA 2760 AGCTGGAAAG GGGCCCATAG GTCATGATGA CATGGTAGAA AGGTTTGGCC TATGTGAAAC 2820 TGAAGAGGAG GAGAGTGAGG ACCAAATTCA AATGGTACCA AGTGATGCCG TCCCAGAAGG 2880 AAAGAACAAA GGCAAGACCA AAAAGGGACG TGGTCGCAAA AATAACTATA ATGCATTCTC 2940 TCGCCGTGGT CTGAGTGATG AAGAATATGA AGAGTACAAA AAGATCAGAG AAGAAAAGAA 3000 TGGCAATTAT AGTATACAAG AATACTTGGA GGACCGCCAA CGATATGAGG AAGAATTAGC 3060 AGAGGTACAG GCAGGTGGTG ATGGTGGCAT AGGAGAAACT GAAATGGAAA TCCGTCACAG 3120 GGTCTTCTAT AAATCCAAGA GTAAGAAACA CCAACAAGAG CAACGGCGAC AACTTGGTCT 3180 AGTGACTGGA TCAGACATCA GAAAACGTAA GCCCATTGAC TGGACCCCGC CAAAGAATGA 3240 ATGGGCAGAT GATGACAGAG AGGTGGATTA TAATGAAAAG ATCAATTTTG AAGCTCCCCC 3300 GACACTATGG AGCCGAGTCA CAAAGTTTGG ATCAGGATGG GGCTTTTGGG TCAGCCGGAC 3360 AGTGTTCATC ACAACCACAC ATGTAGTGCC AACTGGTGTG AAAGAATTCT TTGGTGAGCC 3420 CCTATCTAGT ATAGCAATCC ACCAAGCAGG TGAGTTCACA CAATTCAGGT TCTCAAAGAA 3480 AATGGGCCCT GACTTGACAG GTATGGTCCT TGAAGAAGGT TGCCCTGAAG GGACAGTCTG 3540 CTCAGTCCTA ATTAAACGGG ATTCGGGTGA ACTAGTTCCG CTAGCCGTCC GTATGGGGGC 3600 TATTGCCTCC ATGAGGATAC AGGGTCGGCT TGTCCATGGC CAATCAGGGA TGTTACTGAC 3660 AGGGGCCAAT GCAAAGGGGA TGGATCTTGG CACTATACCA GGAGACTGCG GGGCACCATA 3720 CGTCCACAAG CGCGGGAATG ACTGGGTTGT GTGTGGAGTC CACGCTGCAG CCACAAAGTC 3780 AGGCAACACC GTGGTCTGCG CTGTACAGGC TGGAGAGGGC GAAACCGCAC TAGAAGGTGG 3840 AGACAAGGGG CATTATGCCG GCCACGAGAT TGTGAGGTAT GGAAGTGGCC CAGCACTGTC 3900 AACTAAAACA AAATTCTGGA GGTCCTCCCC AGAACCACTG CCCCCCGGAG TATATGAGCC 3960 AGCATACCTG GGGGGCAAGG ACCCCGGTGT ACAGAATGGC CCATCCCTAC AACAGGTACT 4020 ACGTGACCAA CTGAAACCCT TTGCGGACCC CCGCGGCCGC ATGCCTGAGC CTGGCCTACT 4080 GGAGGCTGCG GTTGAGACTG TAACATCCAT GTTAGAACAG ACAATGGATA CCCCAAGCCC 4140 GTGGTCTTAC GCTGATGCCT GCCAATCTCT TGACAAAACT ACTAGTTCGG GGTACCCTCA 4200 CCATAAAAGG AAGAATGATG ATTGGAATGG CACCAGCTTC GTTGGAGAGC TCGGTGAGCA 4260 AGCTGCACAC GCCAACAATA TGTATGAGAA TGCTAAACAT ATGAAACCCA TTTACACTGC 4320 AGCCTTAAAA GATGAACTAG TCAAGCCAGA AAAGATTTAT CAAAAAGTCA AGAAGCGTCT 4380 ACTATGGGGC GCCGATCTCG GAACAGTGGT CAGGGCCGCC CGGGCTTTTG GCCCCATTTG 4440 TGACGCTATA AAATCACATG TCATCAAATT GCCAATAAAA GTTGGCATGA ACACAATAGA 4500 AGATGGCCCC CTCATCTATG CTGAGCATGC TAAATATAAG AATCATTTTG ATGCAGATTA 4560 TACAGCATGG GACTCAACAC AAAATAGACA AATTATGACA GAATCCTTCT CCATTATGTC 4620 GCGCCTTACG GCCTCACCAG AATTGGCCGA GGTTGTGGCC CAAGATTTGC TAGCACCATC 4680 TGAGATGGAT GTAGGTGATT ATGTCATCAG GGTCAAAGAG GGGCTGCCAT CTGGATTCCC 4740 ATGTACTTCC CAGGTGAACA GCATAAATCA CTGGATAATT ACTCTCTGTG CACTGTCTGA 4800 GGCCACTGGT TTATCACCTG ATGTGGTGCA ATCCATGTCA TATTTCTCAT TTTATGGTGA 4860 TGATGAGATT GTGTCAACTG ACATAGATTT TGACCCAGCC CGCCTCACTC AAATTCTCAA 4920 GGAATATGGC CTCAAACCAA CAAGGCCTGA CAAAACAGAA GGACCAATAC AAGTGAGGAA 4980 AAATGTGGAT GGACTGGTCT TCTTGCGGCG CACCATTTCC CGTGATGCGG CAGGGTTCCA 5040 AGGCAGGTTA GATAGGGCTT CGATTGAACG CCAAATCTTC TGGACCCGCG GGCCCAATCA 5100 TTCAGATCCA TCAGAGACTC TAGTGCCACA CACTCAAAGA AAAATACAGT TGATTTCACT 5160 TCTAGGGGAA GCTTCACTCC ATGGTGAGAA ATTTTACAGA AAGATTTCCA GCAAGGTCAT 5220 ACATGAAATC AAGACTGGTG GATTGGAAAT GTATGTCCCA GGATGGCAGG CCATGTTCCG 5280 CTGGATGCGC TTCCATGACC TCGGATTGTG GACAGGAGAT CGCGATCTTC TGCCCGAATT 5340 CGTAAATGAT GATGGCGTCT AAGGACGCTA CATCAAGCGT GGATGGCGCT AGTGGCGCTG 5400 GTCAGTTGGT ACCGGAGGTT AATGCTTCTG ACCCTCTTGC AATGGATCCT GTAGCAGGTT 5460 CTTCGACAGC AGTCGCGACT GCTGGACAAG TTAATCCTAT TGATCCCTGG ATAATTAATA 5520 ATTTTGTGCA AGCCCCCCAA GGTGAATTTA CTATTTCCCC AAATAATACC CCCGGTGATG 5580 TTTTGTTTGA TTTGAGTTTG GGTCCCCATC TTAATCCTTT CTTGCTCCAT CTATCACAAA 5640 TGTATAATGG TTGGGTTGGT AACATGAGAG TCAGGATTAT GCTAGCTGGT AATGCCTTTA 5700 CTGCGGGGAA GATAATAGTT TCCTGCATAC CCCCTGGTTT TGGTTCACAT AATCTTACTA 5760 TAGCACAAGC AACTCTCTTT CCACATGTGA TTGCTGATGT TAGGACTCTA GACCCCATTG 5820 AGGTGCCTTT GGAAGATGTT AGGAATGTTC TCTTTCATAA TAATGATAGA AATCAACAAA 5880 CCATGCGCCT TGTGTGCATG CTGTACACCC CCCTCCGCAC TGGTGGTGGT ACTGGTGATT 5940 CTTTTGTAGT TGCAGGGCGA GTTATGACTT GCCCCAGTCC TGATTTTAAT TTCTTGTTTT 6000 TAGTCCCTCC TACGGTGGAG CAGAAAACCA GGCCCTTCAC ACTCCCAAAT CTGCCATTGA 6060 GTTCTCTGTC TAACTCACGT GCCCCTCTCC CAATCAGTAG TATGGGCATT TCCCCAGACA 6120 ATGTCCAGAG TGTGCAGTTC CAAAATGGTC GGTGTACTCT GGATGGCCGC CTGGTTGGCA 6180 CCACCCCAGT TTCATTGTCA CATGTTGCCA AGATAAGAGG GACCTCCAAT GGCACTGTAA 6240 TCAACCTTAC TGAATTGGAT GGCACACCCT TTCACCCTTT TGAGGGCCCT GCCCCCATTG 6300 GGTTTCCAGA CCTCGGTGGT TGTGATTGGC ATATCAATAT GACACAGTTT GGCCATTCTA 6360 GCCAGACCCA GTATGATGTA GACACCACCC CTGACACTTT TGTCCCCCAT CTTGGTTCAA 6420 TTCAGGCAAA TGGCATTGGC AGTGGTAATT ATGTTGGTGT TCTTAGCTGG ATTTCCCCCC 6480 CATCACACCC GTCTGGCTCC CAAGTTGACC TTTGGAAGAT CCCCAATTAT GGGTCAAGTA 6540 TTACGGAGGC AACACATCTA GCCCCTTCTG TATACCCCCC TGGTTTCGGA GAGGTATTGG 6600 TCTTTTTCAT GTCAAAAATG CCAGGTCCTG GTGCTTATAA TTTGCCCTGT CTATTACCAC 6660 AAGAGTACAT TTCACATCTT CCTAGTGAAC AAGCCCCTAC TGTAGGTGAG GCTGCCCTGC 6720 TCCACTATGT TGACCCTGAT ACCGGTCGGA ATCTTGGGGA ATTCAAAGCA TACCCTGATG 6780 GTTTCCTCAC TTGTGTCCCC AATGGGGCTA GCTCGGGTCC ACAACAGCTG CCGATCAATG 6840 GGGTCTTTGT CTTTGTTTCA TGGGTGTCCA GATTTTATCA ATTAAAGCCT GTGGGAACTG 6900 CCAGCTCGGC AAGAGGTAGG CTTGGTCTGC GCCGATAATG GCCCAAGCCA TAATTGGTGC 6960 AATTGCTGCT TCCACAGCAG GTAGTGCTCT GGGAGCGGGC ATACAGGTTG GTGGCGAAGC 7020 GGCCCTCCAA AGCCAAAGGT ATCAACAAAA TTTGCAACTG CAAGAAAATT CTTTTAAACA 7080 TGACAGGGAA ATGATTGGGT ATCAGGTTGA AGCTTCAAAT CAATTATTGG CTAAAAATTT 7140 GGCAACTAGA TATTCACTCC TCCGTGCTGG GGGTTTGACC AGTGCTGATG CAGCAAGATC 7200 TGTGGCAGGA GCTCCAGTCA CCCGCATTGT AGATTGGAAT GGCGTGAGAG TGTCTGCTCC 7260 CGAGTCCTCT GCTACCACAT TGAGATCCGG TGGCTTCATG TGAGTTCCCA TACCATTTGC 7320 CTCTAAGCAA AAACAGGTTC AATCATCTGG TATTAGTAAT CCAAATTATT CCCCTTCATC 7380 CATTTCTCGA ACCACTAGTT GGGTCGAGTC ACAAAACTCA TCGAGATTTG GAAATCTTTC 7440 TCCATACCAC GCGGAGGCTC TCAATACAGT GTGGTTGACT CCACCCGGTT CAACAGCCTC 7500 TTCTACACTG TCTTCTGTGC CACGTGGTTA TTTCAATACA GACAGGTTGC CATTATTCGC 7560 AAATAATAGG CGATGATGTT GTAATATGAA ATGTGGGCAT CATATTCATT TAATTAGGTT 7620 TAATTAGGTT TAATTTGATG TTAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA 7680 AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAA 7724

TABLE 2 The amino acid sequence deduced from nucleotides 146 through 5359 of the Norwalk virus genome shown in Table 1. CTCGATAAAG ATAACCAACC AAGAT ATG GCT CTG GGG CTG ATT GGA CAG GTC 172                             Met Ala Leu Gly Leu Ile Gly Gln Val                               1               5 CCA GCG CCA AAG GCC ACA TCC GTC GAT GTC CCT AAA CAA CAG AGG GAT 220 Pro Ala Pro Lys Ala Thr Ser Val Asp Val Pro Lys Gln Gln Arg Asp  10                   15                  20                  25 AGA CCA CCA CGG ACT GTT GCC GAA GTT CAA CAA AAT TTG CGT TGG ACT 268 Arg Pro Pro Arg Thr Val Ala Glu Val Gln Gln Asn Leu Arg Trp Thr                  30                  35                  40 GAG AGA CCA CAA GAC CAG AAT GTT AAG ACG TGG GAT GAG CTT GAC CAC 316 Glu Arg Pro Gln Asp Gln Asn Val Lys Thr Trp Asp Glu Leu Asp His              45                  50                  55 ACA ACA AAA CAA CAG ATA CTT GAT GAA CAC GCT GAG TGG TTT GAT GCC 364 Thr Thr Lys Gln Gln Ile Leu Asp Glu His Ala Glu Trp Phe Asp Ala          60                  65                  70 GGT GGC TTA GGT CCA AGT ACA CTA CCC ACT AGT CAT GAA CGG TAC ACA 412 Gly Gly Leu Gly Pro Ser Thr Leu Pro Thr Ser His Glu Arg Tyr Thr      75                  80                  85 CAT GAG AAT GAT GAA GGC CAC CAG GTA AAG TGG TCG GCT AGG GAA GGT 460 His Glu Asn Asp Glu Gly His Gln Val Lys Trp Ser Ala Arg Glu Gly  90                  95                 100                 105 GTA GAC CTT GGC ATA TCC GGG CTC ACG ACG GTG TCT GGG CCT GAG TGG 508 Val Asp Leu Gly Ile Ser Gly Leu Thr Thr Val Ser Gly Pro Glu Trp                 110                 115                 120 AAT ATG TGC CCG CTA CCA CCA GTT GAC CAA AGG AGC ACG ACA CCT GCA 556 Asn Met Cys Pro Leu Pro Pro Val Asp Gln Arg Ser Thr Thr Pro Ala             125                 130                 135 ACT GAG CCC ACA ATT GGT GAC ATG ATC GAA TTC TAT GAA GGG CAC ATC 604 Thr Glu Pro Thr Ile Gly Asp Met Ile Glu Phe Tyr Glu Gly His Ile         140                 145                 150 TAT CAT TAT GCT ATA TAC ATA GGT CAA GGC AAG ACG GTG GGT GTA CAC 652 Tyr His Tyr Ala Ile Tyr Ile Gly Gln Gly Lys Thr Val Gly Val His     155                 160                 165 TCC CCT CAA GCA CCC TTC TCA ATA ACG AGG ATC ACC ATA CAG CCC ATA 700 Ser Pro Gln Ala Ala Phe Ser Ile Thr Arg Ile Thr Ile Gln Pro Ile 170                 175                 180                 185 TCA GCT TGG TGG CGA GTC TGT TAT GTC CCA CAA CCA AAA CAG AGG CTC 748 Ser Ala Trp Trp Arg Val Cys Tyr Val Pro Gln Pro Lye Gln Arg Leu                 190                 195                 200 ACA TAC GAC CAA CTC AAA GAA TTA GAA AAT GAA CCA TGG CCG TAT GCC 796 Thr Tyr Asp Gln Leu Lys Glu Leu Glu Asn Glu Pro Trp Pro Tyr Ala             205                 210                 215 GCA GTC ACG AAC AAC TGC TTC GAA TTT TGT TGC CAG GTC ATG TGC TTG 844 Ala Val Thr Asn Asn Cys Phe Glu Phe Cys Cys Gln Val Met Cys Leu         220                 225                 230 GAA GAT ACT TGG TTG CAA AGG AAG CTC ATC TCC TCT GGC CGG TTT TAC 892 Glu Asp Thr Trp Leu Gln Arg Lye Leu Ile Ser Ser Gly Arg Phe Tyr     235                 240                 245 CAC CCG ACC CAA GAT TGG TCC CGA GAC ACT CCA GAA TTC CAA CAA GAC 940 His Pro Thr Gln Asp Trp Ser Arg Asp Thr Pro Glu Phe Gln Gln Asp 250                 255                 260                 265 AGC AAG TTA GAG ATG GTT AGG GAT GCA GTG CTA GCC GCT ATA AAT GGG 988 Ser Lys Leu Glu Met Val Arg Asp Ala Val Leu Ala Ala Ile Asn Gly                 270                 275                 280 TTG GTG TCG CGG CCA TTT AAA GAT CTT CTG GGT AAG CTC AAA CCC TTG 1036 Leu Val Ser Arg Pro Phe Lys Asp Leu Leu Gly Lys Leu Lys Pro Leu             285                 290                 295 AAC GTG CTT AAC TTA CTT TCA AAC TGT GAT TGG ACG TTC ATG GGG GTC 1084 Asn Val Leu Asn Leu Leu Ser Asn Cys Asp Trp Thr Phe Met Gly Val         300                 305                 310 GTG GAG ATG GTG GTC CTC CTT TTA GAA CTC TTT GGA ATC TTT TGG AAC 1132 Val Glu Met Val Val Leu Leu Leu Glu Leu Phe Gly Ile Phe Trp Asn     315                 320                 325 CCA CCT GAT GTT TCC AAC TTT ATA GCT TCA CTC CTG CCA GAT TTC CAT 1180 Pro Pro Asp Val Ser Asn Phe Ile Ala Ser Leu Leu Pro Asp Phe His 330                 335                 340                 345 CTA CAG GGC CCC GAG GAC CTT GCC AGG GAT CTC GTG CCA ATA GTA TTG 1228 Leu Gln Gly Pro Glu Asp Leu Ala Arg Asp Leu Val Pro Ile Val Leu                 350                 355                 360 GGG GGG ATC GGC TTA GCC ATA GGA TTC ACC AGA GAC AAG GTA AGT AAG 1276 Gly Gly Ile Gly Leu Ala Ile Gly Phe Thr Arg Asp Lys Val Ser Lys             365                 370                 375 ATG ATG AAG AAT GCT GTT GAT GGA CTT CGT GCG GCA ACC CAG CTC GGT 1324 Met Met Lys Asn Ala Val Asp Gly Leu Arg Ala Ala Thr Gln Leu Gly         380                 385                 390 CAA TAT GGC CTA GAA ATA TTC TCA TTA CTA AAG AAG TAC TTC TTC GGT 1372 Gln Tyr Gly Leu Glu Ile Phe Ser Leu Leu Lys Lys Tyr Phe Phe Gly     395                 400                 405 GGT GAT CAA ACA GAG AAA ACC CTA AAA GAT ATT GAG TCA GCA GTT ATA 1420 Gly Asp Gln Thr Glu Lys Thr Leu Lys Asp Ile Glu Ser Ala Val Ile 410                 415                 420                 425 GAT ATG GAA GTA GTA TCA TCT ACA TCA GTG ACT CAG CTC GTG AGG GAC 1468 Asp Met Glu Val Leu Set Ser Thr Set Val Thr Gln Leu Val Arg Asp                 430                 435                 440 AAA CAG TCT GCA CGG GCT TAT ATG GCC ATC TAA GAT AAT GAA GAA GAA 1516 Lys Gln Ser Ala Arg Ala Tyr Met Ala Ile Leu Asp Asn Glu Glu Glu             445                 450                 455 AAG GCA AGG AAA TTA TCT GTC AGG AAT GCC GAC CCA CAC GTA GTA TCC 1564 Lys Ala Arg Lys Leu Ser Val Arg Asn Ala Asp Pro His Val Val Ser         460                 465                 470 TCT ACC AAT GCT CTC ATA TCC CGG ATC TCA ATG GCT AGG GCT GCA TTG 1612 Ser Thr Asn Ala Leu lIe Ser Arg Ile Ser Met Ala Arg Ala Ala Leu     475                 480                 485 GCC AAG GCT CAA GCT GAA ATG ACC AGC AGG ATG CGT CCT GTG GTC ATT 1660 Ala Lys Ala Gln Ala Glu Met Thr Ser Arg Met Arg Pro Val Val Ile 490                 495                 500                 505 ATG ATG TGT GGG CCC CCT GGT ATA GGT AAA ACC AAG GCA GCA GAA CAT 1708 Met Met Cys Gly Pro Pro Gly Ile Gly Lys Thr Lys Ala Ala Glu His                 510                 515                 520 CTG GCT AAA CGC CTA GCC AAT GAG ATA CGG CCT GGT GGT AAG GTT GGG 1756 Leu Ala Lys Arg Leu Ala Asn Glu Ile Arg Pro Gly Gly Lys Val Gly             525                 530                 535 CTG GTC CCA CGG GAG GCA GTG GAT CAT TGG GAT GGA TAT CAC GGA GAG 1804 Leu Val Pro Arg Glu Ala Val Asp His Trp Asp Gly Tyr Ile Gly Glu         540                 545                 550 GAA GTG ATG CTG TGG GAC GAG TAT GGA ATG ACA AAG ATA CAG GAA GAC 1852 Glu Val Met Leu Trp Asp Asp Tyr Gly Met Thr Lys Ile Gln Glu Asp     555                 560                 565 TGT AAT AAA CTG CAA GCC ATA GCC GAC TCA GCC CCC CTA ACA CTC AAT 1900 Cys Asn Lys Leu Gln Ala Ile Ala Asp Ser Ala Pro Leu Thr Leu Asn 570                 575                 580                 585 TGT GAC CGA ATA GAA AAC AAG GGA ATG CAA TTT GTG TGT GAT GCT ATA 1948 Cys Asp Arg Ile Glu Asn Lys Gly Met Gln Phe Val Ser Asp Ala Ile                 590                 595                 600 GTC ATC ACC ACC AAT GCT CCT GGC CCA GCC CCA GTG GAC TTT GTC AAC 1996 Val Ile Thr Thr Asn Ala Pro Gly Pro Ala Pro Val Asp Phe Val Asn             605                 610                 615 CTC GGG CCT GTT TGC CGA AGG GTG GAC TTC CTT GTG TAT TGC ACG GCA 2044 Leu Gly Pro Val Cys Arg Arg Val Asp Phe Leu Val Tyr Cys Thr Ala         620                 625                 630 CGT GAA GTT GAA CAC ACG AGG AAA GTC AGT CCT GGG GAC ACA ACT GCA 2092 Pro Glu Val Glu His Thr Arg Lys Val Ser Pro Gly Asp Thr Thr Ala     635                 640                 645 CTG AAA GAC TGC TTC AAG CCC GAT TTC TCA CAT CTA AAA ATG GAG TTG 2140 Leu Lys Asp Cys Phe Lys Pro Asp Phe Ser His Leu Lys Met Glu Leu 650                 655                 660                 665 GCT CCC CAA GGG GGC TTT GAT AAC CAA GGG AAT ACC CCG TTT GGT AAG 2188 Ala Pro Gln Gly Gly Phe Asp Asn Gln Gly Asn Thr Pro Phe Gly Lys                 670                 675                 680 GGT GTG ATG AAG CCC ACC ACC ATA AAC AGG CTG TTA ATC CAG GCT GTA 2236 Gly Val Met Lys Pro Thr Thr Ile Asn Arg Leu Leu Ile Gln Ala Val             685                 690                 695 GCC TTG ACG ATG GAG AGA CAG GAT GAG TTC CAA CTC CAG GGG CCT ACG 2284 Ala Leu Thr Met Glu Arg Gln Asp Glu Phe Gln Leu Gln Gly Pro Thr         700                 705                 710 TAT GAC TTT GAT ACT GAC AGA GTA GCT GCG TTC ACG AGG ATG GCC CGA 2332 Tyr Asp Phe Asp Thr Asp Arg Val Ala Ala Phe Thr Arg Met Ala Arg     715                 720                 725 GCC AAC GGG TTG GGT CTC ATA TCC ATG GCC TCC CTA GGC AAA AAG CTA 2380 Ala Asn Gly Leu Gly Leu Ile Ser Met Ala Ser Leu Gly Lys Lys Leu 730                 735                 740                 745 CGC AGT GTC ACC ACT ATT GAA GGA TTA AAG AAT GCT CTA TCA GGC TAT 2428 Arg Ser Val Thr Thr Ile Glu Gly Leu Lys Asn Ala Leu Ser Gly Tyr                 750                 755                 760 AAA ATA TCA AAA TGC AGT ATA CAA TGG CAG TCA AGG GTG TAC ATT ATA 2476 Lys Ile Ser Lys Cys Ser Ile Gln Trp Gln Ser Arg Val Tyr Ile Ile             765                 770                 775 GAA TCA GAT GGT GCC AGT GTA CAA ATC AAA GAA GAC AAG CAA GCT TTG 2524 Glu Ser Asp Gly Ala Ser Val Gln Ile Lys Glu Asp Lys Gln Ala Leu         780                 785                 790 ACC CCT CTG CAG CAG ACA ATT AAC ACG GCC TCA CTT GCC ATC ACT CGA 2572 Thr Pro Leu Gln Gln Thr Ile Asn Thr Ala Ser Leu Ala Ile Thr Arg     795                 800                 805 CTC AAA GCA GCT AGG GCT GTG GCA TAC GCT TCA TGT TTC CAG TCC GCC 2620 Leu Lys Ala Ala Arg Ala Val Ala Tyr Ala Ser Cys Phe Gln Ser Ala 810                 815                 820                 825 ATA ACT ACC ATA CTA CAA ATG GCG GGA TCT GCG CTC GTT ATT AAT CGA 2668 Ile Thr Thr Ile Leu Gln Met Ala Gly Ser Ala Leu Val Ile Asn Arg                 830                  835                 840 GCG GTC AAG CGT ATG TTT GGT ACC CGT ACA GCA GCC ATG GCA TTA GAA 2716 Ala Val Lys Arg Met Phe Gly Thr Arg Thr Ala Ala Met Ala Leu Glu             845                 850                 855 GGA CCT GGG AAA GAA CAT AAT TGC AGG GTC CAT AAG GCT AAG GAA GCT 2764 Gly Pro Gly Lys Glu His Asn Cys Arg Val His Lys Ala Lys Glu Ala         860                 865                 870 GGA AAG GGG CCC ATA GGT CAT GAT GAC ATG GTA GAA AGG TTT GCC CTA 2812 Gly Lys Gly Pro Ile Gly His Asp Asp Met Val Glu Arg Phe Gly Leu     875                 880                 885 TGT GAA ACT GAA GAG GAG GAG AGT GAG GAC CAA ATT CAA ATG GTA CCA 2860 Cys Glu Thr Glu Glu Glu Glu Ser Glu Asp Gln Ile Gln Met Val Pro 890                 895                 900                 905 ACT GAT GCC GTC CCA GAA GGA AAG AAC AAA GGC AAG ACC AAA AAG GGA 2908 Ser Asp Ala Val Pro Glu Gly Lys Asn Lys Gly Lys Thr Lys Lys Gly                     910             915                 920 CGT GGT CGC AAA AAT AAC TAT AAT GCA TTC TCT CGC CGT GGT CTG AGT 2956 Arg Gly Arg Lys Asn Asn Tyr Asn Ala Phe Ser Arg Arg Gly Leu Ser             925                 930                 935 GAT GAA GAA TAT GAA GAG TAC AAA AAG ATC AGA GAA GAA AAG AAT GGC 3004 Asp Glu Glu Tyr Glu Glu Tyr Lys Lys Ile Arg Glu Glu Lys Asn Gly         940                 945                 950 AAT TAT AGT ATA CAA GAA TAC TTG GAG GAC CGC CAA CGA TAT GAG GAA 3052 Asn Tyr Ser Ile Gln Glu Tyr Leu Clu Asp Arg Gln Arg Tyr Glu Glu     955                 960                 965 GAA TTA GCA GAG GTA CAG GCA GGT GGT GAT GGT GGC ATA GGA GAA ACT 3100 Glu Leu Ala Glu Val Gln Ala Gly Gly Asp Gly Gly Ile Gly Glu Thr 970                 975                 980                 985 GAA ATG GAA ATC CGT CAC AGG GTC TTC TAT AAA TCC AAG AGT AAG AAA 3148 Glu Met Glu Ile Arg His Arg Val Phe Tyr Lys Ser Lys Ser Lys Lys                 990                 995                 1000 CAC CAA CAA GAG CAA CGG CGA CAA CTT GGT CTA GTG ACT GGA TCA GAC 3196 His Gln Gln Glu Gln Arg Arg Gln Leu Gly Leu Val Thr Gly Ser Asp             1005                1010                1015 ATC AGA AAA CGT AAG CCC ATT GAC TGG ACC CCG CCA AAG AAT GAA TGG 3244 Ile Arg Lys Arg Lys Pro Ile Asp Trp Thr Pro Pro Lys Asn Glu Trp         1020                1025                1030 GCA GAT GAT GAC AGA GAG GTG GAT TAT AAT GAA AAG ATC AAT TTT GAA 3292 Ala Asp Asp Asp Arg Glu Val Asp Tyr Asn Glu Lys Ile Asn Phe Glu 1035                1040                1045 GCT CCC CCG ACA CTA TGG AGC CGA GTC ACA AAG TTT GGA TCA GGA TGG 3340 Ala Pro Pro Thr Leu Trp Ser Arg Val Thr Lys Phe Gly Ser Gly Trp 1050                1055                1060                1065 GGC TTT TGG GTC AGC CCG ACA GTG TTC ATC ACA ACC ACA CAT GTA GTG 3388 Gly Phe Trp Val Ser Pro Thr Val Phe Ile Thr Thr Thr His Val Val                 1070                1075                1080 CCA ACT GGT GTG AAA GAA TTC TTT GGT GAG CCC CTA TCT AGT ATA GCA 3436 Pro Thr Gly Val Lys Glu Phe Phe Gly Glu Pro Leu Ser Ser Ile Ala             1085                1090                1095 ATC CAC CAA GCA GGT GAG TTC ACA CAA TTC AGG TTC TCA AAG AAA ATG 3484 Ile His Gln Ala Gly Glu Phe Thr Gln Phe Arg Phe Ser Lys Lys Met         1100                1105                1110 CGC CCT GAC TTG ACA GGT ATG GTC CTT GAA GAA GGT TGC CCT GAA GGG 3532 Arg Pro Asp Leu Thr Gly Met Val Leu Glu Glu Gly Cys Pro Glu Gly     1115                1120                1125 ACA GTC TGC TCA GTC CTA ATT AAA CGG GAT TCG GGT GAA CTA CTT CCG 3580 Thr Val Cys Ser Val Leu Ile Lys Arg Asp Ser Gly Glu Leu Leu Pro 1130                1135                1140                1145 CTA GCC GTC CGT ATG GGG GCT ATT GCC TCC ATG AGG ATA CAG GGT CGG 3628 Leu Ala Val Arg Met Gly Ala Ile Ala Ser Met Arg Ile Gln Gly Arg                 1150                1155                1160 CTT GTC CAT GGC CAA TCA GGG ATG TTA CTG ACA GGG GCC AAT GCA AAG 3676 Leu Val His Gly Gln Ser Gly Met Leu Leu Thr Gly Ala Asn Ala Lys             1165                1170                1175 GGG ATG GAT CTT GGC ACT ATA CCA GGA GAC TGC GGG GCA CCA TAC GTC 3724 Gly Met Asp Leu Gly Thr Ile Pro Gly Asp Cys Gly Ala Pro Tyr Val         1180                1185                1190 CAC AAG CGC GGG AAT GAG TGG GTT GTG TGT GGA GTC CAC GCT GCA GCC 3772 His Lys Arg Gly Asn Asp Trp Val Val Cys Gly Val His Ala Ala Ala     1195                1200                1205 ACA AAG TCA GGC AAC ACC GTG GTC TGC GCT GTA CAG GCT GGA GAG GGC 3820 Thr Lys Ser Gly Asn Thr Val Val Cys Ala Val Gln Ala Gly Glu Gly 1210                1215                1220                1225 GAA ACC GCA CTA GAA GGT GGA GAC AAG GGG CAT TAT GCC GGC CAC GAG 3868 Glu Thr Ala Leu Glu Gly Gly Asp Lys Gly His Tyr Ala Gly His Glu                 1230                1235                1240 ATT GTG AGG TAT GGA AGT GGC CCA GCA CTG TCA ACT AAA ACA AAA TTC 3916 Ile Val Arg Tyr Gly Ser Gly Pro Ala Leu Ser Thr Lys Thr Lys Phe             1245                1250                1255 TGG AGG TCC TCC CCA GAA CCA CTG CCC CCC GGA GTA TAT GAG CCA GCA 3964 Trp Arg Ser Ser Pro Glu Pro Leu Pro Pro Gly Val Tyr Glu Pro Ala 1260                        1265                1270 TAC CTG GGG GGC AAG GAC CCC CGT GTA CAG AAT GGC CCA TCC CTA CAA 4012 Tyr Leu Gly Gly Lys Asp Pro Arg Val Gln Asn Gly Pro Ser Leu Gln     1275                1280                1285 CAG GTA CTA CGT GAC CAA CTG AAA CCC TTT GCG GAG CCC CGC GGC CGC 4060 Gln Val Leu Arg Asp Gln Leu Lys Pro Phe Ala Asp Pro Arg Gly Arg 1290                1295                1300                1305 ATG CCT GAG CCT GGC CTA CTG GAG GCT GCG GTT GAG ACT GTA ACA TCC 4108 Met Pro Glu Pro Gly Leu Leu Glu Ala Ala Val Glu Thr Val Thr Ser                 1310                1315                1320 ATG TTA GAA CAG ACA ATG GAT ACC CCA AGC CCG TGG TCT TAC GCT GAT 4156 Met Leu Glu Gln Thr Met Asp Thr Pro Ser Pro Trp Ser Tyr Ala Asp             1325                1330                1335 GCC TGC CAA TCT CTT GAC AAA ACT ACT AGT TCG GGG TAC CCT CAC CAT 4204 Ala Cys Gln Ser Leu Asp Lys Thr Thr Ser Ser Gly Tyr Pro His His         1340                1345                1350 AAA AGG AAG AAT GAT GAT TGG AAT GGC ACC ACC TTC GTT GGA GAG CTC 4252 Lys Arg Lys Asn Asp Asp Trp Asn Gly Thr Thr Phe Val Gly Glu Leu     1355                1360                1365 GGT GAG CAA GCT GCA CAC GCC AAC AAT ATG TAT GAG AAT GCT AAA CAT 4300 Gly Glu Gln Ala Ala His Ala Asn Asn Met Tyr Glu Asn Ala Lys His 1370                1375                1380                1385 ATG AAA CCC ATT TAC ACT GCA GCC TTA AAA GAT GAA CTA GTC AAG CCA 4348 Met Lys Pro Ile Tyr Thr Ala Ala Leu Lys Asp Glu Leu Val Lys Pro                 1390                1395                1400 GAA AAG ATT TAT CAA AAA GTC AAG AAG CGT CTA CTA TGG GGC GCC GAT 4396 Glu Lys Ile Tyr Gln Lys Val Lys Lys Arg Leu Leu Trp Gly Ala Asp             1405                1410                1415 CTC GGA ACA GTG GTC AGG GCC GCC CGG GCT TTT GGC CCA TTT TGT GAC 4444 Leu Gly Thr Val Val Arg Ala Ala Arg Ala Phe Gly Pro Phe Cys Asp         1420                1425                1430 GCT ATA AAA TCA CAT GTC ATC AAA TTG CCA ATA AAA GTT GGC ATG AAC 4492 Ala Ile Lys Ser His Val Ile Lys Leu Pro Ile Lys Val Gly Met Asn     1435                1440                1445 ACA ATA GAA GAT GGC CCC CTC ATC TAT GCT GAG CAT GCT AAA TAT AAG 4540 Thr Ile Glu Asp Gly Pro Leu Ile Tyr Ala Glu His Ala Lys Tyr Lys 1450                1455                1460                1465 AAT CAT TTT GAT GCA GAT TAT ACA GCA TGG GAC TCA ACA CAA AAT AGA 4588 Asn His Phe Asp Ala Asp Tyr Thr Ala Trp Asp Ser Thr Gln Asn Arg                 1470                1475                1480 CAA ATT ATG ACA GAA TCC TTC TCC ATT ATG TCG CGC CTT ACG GCC TCA 4636 Gln Ile Met Thr Glu Ser Phe Ser Ile Met Ser Arg Leu Thr Ala Ser             1485                1490                1495 CCA GAA TTG GCC GAG GTT GTG GCC CAA GAT TTG CTA GCA CCA TCT GAG 4684 Pro Glu Leu Ala Glu Val Val Ala Gln Asp Leu Leu Ala Pro Ser Glu         1500                1505                1510 ATG GAT GTA GGT GAT TAT GTC ATC AGG GTC AAA GAG GGG CTG CCA TCT 4732 Met Asp Val Gly Asp Tyr Val Ile Arg Val Lys Glu Gly Leu Pro Ser     1515                1520                1525 GGA TTC CCA TGT ACT TCC CAG GTG AAC AGC ATA AAT CAC TGG ATA ATT 4780 Gly Phe Pro Cys Thr Ser Gln Val Asn Ser Ile Asn His Trp Ile Ile 1530                1535                1540                1545 ACT CTC TGT GCA CTG TCT GAG GCC ACT GGT TTA TCA CCT GAT GTG GTG 4828 Thr Leu Cys Ala Leu Ser Glu Ala Thr Gly Leu Ser Pro Asp Val Val                 1550                1555                1560 CAA TCC ATG TCA TAT TTC TCA TTT TAT GGT GAT GAT GAG ATT GTG TCA 4876 Gln Ser Met Ser Tyr Phe Ser Phe Tyr Gly Asp Asp Glu Ile Val Ser             1565                1570                1575 ACT GAC ATA GAT TTT GAC CCA GCC CGC CTC ACT CAA ATT CTC AAG GAA 4924 Thr Asp Ile Asp Phe Asp Pro Ala Arg Leu Thr Gln Ile Leu Lys Glu         1580                1585                1590 TAT GGC CTC AAA CCA ACA AGG CCT GAC AAA ACA GAA GGA CCA ATA CAA 4972 Tyr Gly Leu Lys Pro Thr Arg Pro Asp Lys Thr Glu Gly Pro Ile Gln     1595                1600                1605 GTG AGG AAA AAT GTG GAT GGA CTG GTC TTC TTG CGG CGC ACC ATT TCC 5020 Val Arg Lys Asn Val Asp Gly Leu Val Phe Leu Arg Arg Thr Ile Ser 1610                1615                1620                1625 CGT GAT GCG GCA GGG TTC CAA GGC AGG TTA GAT AGG GCT TCG ATT GAA 5068 Arg Asp Ala Ala Gly Phe Gln Gly Arg Leu Asp Arg Ala Ser Ile Glu                 1630                1635                1640 CGC CAA ATC TTC TGG ACC CGC GGG CCC AAT CAT TCA GAT CCA TCA GAG 5116 Arg Gln Ile Phe Trp Thr Arg Gly Pro Asn His Ser Asp Pro Ser Glu             1645                1650                1655 ACT CTA GTG CCA CAC ACT CAA AGA AAA ATA CAG TTG ATT TCA CTT CTA 5164 Thr Leu Val Pro His Thr Gln Arg Lys Ile Gln Leu Ile Ser Leu Leu         1660                1665                1670 GGG GAA GCT TCA CTC CAT GGT GAG AAA TTT TAC AGA AAG ATT TCC AGC 5212 Gly Glu Ala Ser Leu His Gly Glu Lys Phe Tyr Arg Lys Ile Ser Ser     1675                1680                1685 AAG GTC ATA CAT GAA ATC AAG ACT GGT GGA TTG GAA ATG TAT GTC CCA 5260 Lys Val Ile His Glu Ile Lys Thr Gly Gly Leu Glu Met Tyr Val Pro 1690                1695                1700                1705 GGA TGG CAG GCC ATG TTC CGG TGG ATG CGC TTC CAT GAC CTC GGA TTG 5308 Gly Trp Gln Ala Met Phe Arg Trp Met Arg Phe His Asp Leu Gly Leu                 1710                1715                1720 TGG ACA GGA GAT CGG GAT CTT CTG CCC GAA TTC GTA AAT GAT GAT GGC 5356 Trp Thr Gly Asp Arg Asp Leu Leu Pro Glu Phe Val Asn Asp Asp Gly             1725                1730                1735 GTC TAAGGACGCT ACATCAAGCG TGGATGGCGC TAGTGGCGCT GGTCAGTTGG 5409 Val

TABLE 3 The amino acid sequence deduced from nucleotides 5346 through 6935 of the Norwalk virus genome shown in Table 1. CGTAA ATG ATG ATG GCG TCT AAG GAC GCT ACA TCA AGC GTG GAT GGC 5387       Met Met Met Ala Ser Lys Asp Ala Thr Ser Ser Val Asp Gly         1               5                  10 GCT AGT GGC GCT GGT CAG TTG GTA CCG GAG GTT AAT GCT TCT GAC CCT 5435 Ala Ser Gly Ala Gly Gln Leu Val Pro Glu Val Asn Ala Ser Asp Pro  15                  20                  25                  30 CTT GCA ATG GAT CCT GTA GCA GGT TCT TCG ACA GCA GTC GCG ACT GCT 5483 Leu Ala Met Asp Pro Val Ala Gly Ser Ser Thr Ala Val Ala Thr Ala                  35                  40                  45 GGA CAA GTT AAT CCT ATT GAT CCC TGG ATA ATT AAT AAT TTT GTG CAA 5531 Gly Gln Val Asn Pro Ile Asp Pro Trp Ile Ile Asn Asn Phe Val Gln              50                  55                  60 GCC CCC CAA GGT GAA TTT ACT ATT TCC CCA AAT AAT ACC CCC GGT GAT 5579 Ala Pro Gln Gly Glu Phe Thr Ile Ser Pro Asn Asn Thr Pro Gly Asp          65                  70                  75 GTT TTG TTT GAT TTG AGT TTG GGT CCC CAT CTT AAT CCT TTC TTG CTC 5627 Val Leu Phe Asp Leu Ser Leu Gly Pro His Leu Asn Pro Phe Leu Leu      80                  85                  90 CAT CTA TCA CAA ATG TAT AAT GGT TGG GTT GGT AAC ATG AGA GTC AGG 5675 His Leu Ser Gln Met Tyr Asn Gly Trp Val Gly Asn Met Arg Val Arg  95                 100                 105                 110 ATT ATG CTA GCT GGT AAT CCC TTT ACT GCG GGG AAG ATA ATA GTT TCC 5723 Ile Met Leu Ala Gly Asn Ala Phe Thr Ala Gly Lys Ile Ile Val Ser                 115                 120                 125 TGC ATA CCC CCT GGT TTT GGT TCA CAT AAT CTT ACT ATA GCA CAA GCA 5771 Cys Ile Pro Pro Gly Phe Gly Ser His Asn Leu Thr Ile Ala Gln Ala             130                 135                 140 ACT CTC TTT CCA CAT GTG ATT GCT GAT GTT AGG ACT CTA GAC CCC ATT 5819 Thr Leu Phe Pro His Val Ile Ala Asp Val Arg Thr Leu Asp Pro Ile         145                 150                 155 GAG GTG CCT TTG GAA GAT GTT AGG AAT GTT CTC TTT CAT AAT AAT GAT 5867 Glu Val Pro Leu Glu Asp Val Arg Asn Val Leu Phe His Asn Asn Asp     160                 165                 170 AGA AAT CAA CAA ACC ATG CGC CTT GTG TGC ATG CTG TAC ACC CCC CTC 5915 Arg Asn Gln Gln Thr Met Arg Leu Val Cys Met Leu Tyr Thr Pro Leu 175                 180                 185                 190 CGC ACT GGT GGT GGT ACT GGT GAT TGT TTT GTA GTT GCA GGG CGA GTT 5963 Arg Thr Gly Gly Gly Thr Gly Asp Ser Phe Val Val Ala Gly Arg Val                 195                 200                 205 ATG ACT TGC CCC AGT CCT GAT TTT AAT TTC TTG TTT TTA GTC CGT CCT 6011 Met Thr Cys Pro Ser Pro Asp Phe Asn Phe Leu Phe Leu Val Pro Pro             210                 215                 220 ACG GTG GAG CAG AAA ACC AGG CCC TTC ACA CTC CCA AAT CTG CCA TTG 6059 Thr Val Glu Gln Lys Thr Arg Pro Phe Thr Leu Pro Asn Leu Pro Leu         225                 230                 235 AGT TCT CTG TCT AAC TCA CGT GCC CCT CTC CCA ATC AGT AGT ATG GGC 6107 Ser Ser Leu Ser Asn Ser Arg Ala Pro Leu Pro Ile Ser Ser Met Gly     240                 245                 250 ATT TCC CCA GAC AAT GTC CAG AGT GTG CAG TTC CAA AAT GGT CGG TGT 6155 Ile Ser Pro Asp Asn Val Gln Ser Val Gln Phe Gln Asn Gly Arg Cys 255                 260                 265                 270 ACT CTG GAT GGC CGC CTG GTT GGC ACC ACC CCA GTT TCA TTG TCA CAT 6203 Thr Leu Asp Gly Arg Leu Val Gly Thr Thr Pro Val Ser Leu Ser His                 275                 280                 285 GTT GCC AAG ATA AGA GGG ACC TCC AAT GGC ACT GTA ATC AAC CTT ACT 6251 Val Ala Lys Ile Arg Gly Thr Ser Asn Gly Thr Val Ile Asn Leu Thr             290                 295                 300 GAA TTG GAT GGC ACA CCC TTT CAC CCT TTT GAG GGC CCT GCC CCC ATT 6299 Glu Leu Asp Gly Thr Pro Phe His Pro Phe Glu Gly Pro Ala Pro Ile         305                 310                 315 GGG TTT CCA GAC CTC GGT GGT TGT GAT TGG CAT ATC AAT ATG ACA CAG 6347 Gly Phe Pro Asp Leu Gly Gly Cys Asp Trp His Ile Asn Met Thr Gln     320                 325                 330 TTT GGC CAT TCT AGC CAG ACC CAG TAT GAT GTA GAC ACC ACC CCT GAC 6395 Phe Gly His Ser Ser Gln Thr Gln Tyr Asp Val Asp Thr Thr Pro Asp 335                 340                 345                 350 ACT TTT GTC CCC CAT CTT GGT TCA ATT CAG GCA AAT GGC ATT GGC AGT 6443 Thr Phe Val Pro His Leu Gly Ser Ile Gln Ala Asn Gly Ile Gly Ser                 355                 360                 365 GGT AAT TAT GTT GGT GTT GTT AGC TGG ATT TCC CCC CCA TCA CAC CCG 6491 Gly Asn Tyr Val Gly Val Leu Ser Trp Ile Ser Pro Pro Ser His Pro             370                 375                 380 TCT GGC TCC CAA GTT GAC CTT TGG AAG ATC CCC AAT TAT GGG TCA AGT 6539 Ser Gly Ser Gln Val Asp Leu Trp Lys Ile Pro Asn Tyr Gly Ser Ser         385                 390                 395 ATT ACG GAG GCA ACA CAT CTA GCC CCT TCT GTA TAC CCC CGT GGT TTC 6587 Ile Thr Glu Ala Thr His Leu Ala Pro Ser Val Tyr Pro Pro Gly Phe     400                 405                 410 GGA GAG GTA TTG GTC TTT TTC ATG TCA AAA ATG CCA GGT CCT GGT GCT 6635 Gly Glu Val Leu Val Phe Phe Met Ser Lys Met Pro Gly Pro Gly Ala 415                 420                 425                 430 TAT AAT TTG CCC TGT CTA TTA CCA CAA GAG TAC ATT TCA CAT CTT GCT 6683 Tyr Asn Leu Pro Cys Leu Leu Pro Gln Glu Tyr Ile Ser His Leu Ala                 435                 440                 445 AGT GAA CAA GCC CCT ACT GTA GGT GAG GCT GCC CTG CTC CAC TAT GTT 6731 Ser Glu Gln Ala Pro Thr Val Gly Glu Ala Ala Leu Leu His Tyr Val             450                 455                 460 GAC CCT GAT ACC GGT CGG AAT CTT GGG GAA TTC AAA GCA TAC CCT GAT 6779 Asp Pro Asp Thr Gly Arg Asn Leu Gly Glu Phe Lys Ala Tyr Pro Asp         465                 470                 475 GGT TTC CTC ACT TGT GTC CCC AAT GGG GCT AGC TCG GGT CCA CAA CAG 6827 Gly Phe Leu Thr Cys Val Pro Asn Gly Ala Ser Ser Gly Pro Gln Gln     480                 485                 490 CTG CCG ATC AAT GGG GTC TTT GTC TTT GTT TCA TGG GTG TCC AGA TTT 6875 Leu Pro Ile Asn Gly Val Phe Val Phe Val Ser Trp Val Ser Arg Phe 495                 500                 505                 510 TAT CAA TTA AAG CCT GTG GGA ACT GCC AGC TCG GCA AGA GGT AGG CTT 6923 Tyr Gln Leu Lys Pro Val Gly Thr Ala Ser Ser Ala Arg Gly Arg Leu                 515                 520                 525 GGT CTG CGC CGA TAATGGCCCA AGCCATAATT GGTGCAATTG CTGCTTCCAC 6975 Gly Leu Arg Arg             530

TABLE 4 The amino acid sequence deduced from nucleotides 6938 through 7573 of the Norwalk virus genome shown in Table 1. CCAGCTCGGC AAGAGGTAGG CTTGGTCTGC GCCGATA ATG GCC CAA GCC ATA ATT 6955 Met Ala Gln Ala Ile Ile 1 5 GGT GCA ATT GCT GCT TCC ACA GCA GGT AGT GCT CTG GGA GCG GGC ATA 7003 Gly Ala Ile Ala Ala Ser Thr Ala Gly Ser Ala Leu Gly Ala Gly Ile 10 15 20 CAG GTT GGT GGC GAA GCG GCC CTC CAA AGC CAA AGG TAT CAA CAA AAT 7051 Gln Val Gly Gly Glu Ala Ala Leu Gln Ser Gln Arg Tyr Gln Gln Asn 25 30 35 TTG CAA CTG CAA GAA AAT TCT TTT AAA CAT GAC AGG GAA ATG ATT GGG 7099 Leu Gln Leu Gln Glu Asn Ser Phe Lys His Asp Arg Glu Met Ile Gly 40 45 50 TAT CAG GTT GAA GCT TCA AAT CAA TTA TTG GCT AAA AAT TTG GCA ACT 7147 Tyr Gln Val Glu Ala Ser Asn Gln Leu Leu Ala Lys Asn Leu Ala Thr 55 60 65 70 AGA TAT TCA CTC CTC CGT GCT GGG GGT TTG ACC AGT GCT CAT GCA GCA 7195 Arg Tyr Ser Leu Leu Arg Ala Gly Gly Leu Thr Ser Ala Asp Ala Ala 75 80 85 AGA TCT GTG GCA GGA GCT CCA GTC ACC CGC ATT GTA GAT TGG AAT GGC 7243 Arg Ser Val Ala Gly Ala Pro Val Thr Arg Ile Val Asp Trp Asn Gly 90 95 100 GTG AGA GTG TCT GCT CCC GAG TCC TCT GCT ACC ACA TTG AGA TCC GGT 7291 Val Arg Val Ser Ala Pro Glu Ser Ser Ala Thr Thr Leu Arg Ser Gly 105 110 115 GGC TTC ATG TCA GTT CCC ATA CCA TTT GCC TCT AAG CAA AAA CAG GTT 7339 Gly Phe Met Ser Val Pro Ile Pro Phe Ala Ser Lys Gln Lys Gln Val 120 125 130 CAA TCA TCT GGT ATT ACT AAT CCA AAT TAT TCC CCT TCA TCC ATT TCT 7387 Gln Ser Ser Gly Ile Ser Asn Pro Asn Tyr Ser Pro Ser Ser Ile Ser 135 140 145 150 CGA ACC ACT AGT TGG GTC GAG TCA CAA AAC TCA TCG AGA TTT GGA AAT 7435 Arg Thr Thr Ser Trp Val Glu Ser Gln Asn Ser Ser Arg Phe Gly Asn 155 160 165 CTT TCT CCA TAC CAC GCG GAG GCT CTC AAT ACA GTG TGG TTG ACT CCA 7483 Leu Ser Pro Tyr His Ala Glu Ala Leu Asn Thr Val Trp Leu Thr Pro 170 175 180 CCC GGT TCA ACA GCC TCT TCT ACA CTG TCT TCT GTG CCA CGT GGT TAT 7531 Pro Gly Ser Thr Ala Ser Ser Thr Leu Ser Ser Val Pro Arg Gly Tyr 185 190 195 TTC AAT ACA GAC AGG TTG CCA TTA TTC GCA AAT AAT AGG CGA 7573 Phe Asn Thr Asp Arg Leu Pro Leu Phe Ala Asn Asn Arg Arg 200 205 210 

1. A method of inducing an immune response against Norwalk virus in an animal comprising the step of administering to the animal an effective amount of a composition having a purified Norwalk virus immunogen that forms a stable virus-like particle lacking nucleic acids, wherein the immunogen is produced in an expression system using the nucleotide sequence of SEQ. ID. NO.1.
 2. The method of claim 1, wherein the immunogen is produced in an expression system using nucleotides 5337 through 7724 of SEQ. ID. NO.1.
 3. The method of claim 1, wherein the composition is administered orally.
 4. The method of claim 1, wherein the composition is administered parenterally.
 5. The method of claim 1, wherein the virus-like particle is non-infectious.
 6. The method of claim 3, wherein the composition is administered subsequent to oral administration of sodium bicarbonate.
 7. The method of claim 3, wherein the composition is administered prior to oral administration of sodium bicarbonate.
 8. The method of claim 3, wherein sodium bicarbonate is administered orally following administration of the composition. 